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 $93.57   3.329%   $96.6849   $96.68   $96.70   $96.70  
  Purchase #2 $140.73   10.483%   $155.4827   $155.48   $155.50   $155.50  
  Purchase #3 $225.45   9.644%   $247.1924   $247.19   $247.20   $247.20  
  Purchase #4 $106.71   12.142%   $119.6667   $119.67   $119.65   $119.70  
  Purchase #5 $154.30   3.866%   $160.2652   $160.27   $160.25   $160.30  
  Purchase #6 $167.53   4.522%   $175.1057   $175.11   $175.10   $175.10  
  Purchase #7 $65.70   5.542%   $69.3411   $69.34   $69.35   $69.30  
  7 purchase totals = $953.99       $1,023.7387   $1,023.74   $1,023.75   $1,023.80