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 $87.83   6.561%   $93.5925   $93.59   $93.60   $93.60  
  Purchase #2 $86.66   8.493%   $94.02   $94.02   $94.00   $94.00  
  Purchase #3 $217.25   12.119%   $243.5785   $243.58   $243.60   $243.60  
  Purchase #4 $63.37   13.200%   $71.7348   $71.73   $71.75   $71.70  
  Purchase #5 $169.41   11.855%   $189.4936   $189.49   $189.50   $189.50  
  Purchase #6 $96.30   7.560%   $103.5803   $103.58   $103.60   $103.60  
  Purchase #7 $208.44   8.261%   $225.6592   $225.66   $225.65   $225.70  
  7 purchase totals = $929.26       $1,021.6589   $1,021.65   $1,021.70   $1,021.70