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 $246.27   12.146%   $276.182   $276.18   $276.20   $276.20  
  Purchase #2 $36.57   9.593%   $40.0782   $40.08   $40.10   $40.10  
  Purchase #3 $63.92   4.170%   $66.5855   $66.59   $66.60   $66.60  
  Purchase #4 $24.88   5.353%   $26.2118   $26.21   $26.20   $26.20  
  Purchase #5 $61.59   7.363%   $66.1249   $66.12   $66.10   $66.10  
  Purchase #6 $32.43   3.561%   $33.5848   $33.58   $33.60   $33.60  
  Purchase #7 $91.98   4.621%   $96.2304   $96.23   $96.25   $96.20  
  7 purchase totals = $557.64       $604.9976   $604.99   $605.05   $605.00