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 $48.33   7.630%   $52.0176   $52.02   $52.00   $52.00  
  Purchase #2 $248.38   8.731%   $270.0661   $270.07   $270.05   $270.10  
  Purchase #3 $224.52   8.499%   $243.602   $243.60   $243.60   $243.60  
  Purchase #4 $49.75   3.635%   $51.5584   $51.56   $51.55   $51.60  
  Purchase #5 $111.80   4.617%   $116.9618   $116.96   $116.95   $117.00  
  Purchase #6 $5.64   10.361%   $6.2244   $6.22   $6.20   $6.20  
  Purchase #7 $250.63   12.232%   $281.2871   $281.29   $281.30   $281.30  
  7 purchase totals = $939.05       $1,021.7174   $1,021.72   $1,021.65   $1,021.80