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 $48.71   7.634%   $52.4285   $52.43   $52.45   $52.40  
  Purchase #2 $212.96   10.520%   $235.3634   $235.36   $235.35   $235.40  
  Purchase #3 $158.94   13.528%   $180.4414   $180.44   $180.45   $180.40  
  Purchase #4 $195.45   11.419%   $217.7684   $217.77   $217.75   $217.80  
  Purchase #5 $150.96   11.444%   $168.2359   $168.24   $168.25   $168.20  
  Purchase #6 $179.92   6.693%   $191.962   $191.96   $191.95   $192.00  
  Purchase #7 $138.48   7.810%   $149.2953   $149.30   $149.30   $149.30  
  7 purchase totals = $1,085.42       $1,195.4949   $1,195.50   $1,195.50   $1,195.50