Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $165.36   10.621%   $182.9229   $182.92   $182.90   $182.90  
  Purchase #2 $156.58   5.857%   $165.7509   $165.75   $165.75   $165.80  
  Purchase #3 $238.71   11.167%   $265.3667   $265.37   $265.35   $265.40  
  Purchase #4 $208.83   10.362%   $230.469   $230.47   $230.45   $230.50  
  Purchase #5 $111.98   9.468%   $122.5823   $122.58   $122.60   $122.60  
  Purchase #6 $167.66   6.229%   $178.1035   $178.10   $178.10   $178.10  
  Purchase #7 $133.33   11.169%   $148.2216   $148.22   $148.20   $148.20  
  7 purchase totals = $1,182.45       $1,293.4169   $1,293.41   $1,293.35   $1,293.50