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 $84.83   10.758%   $93.956   $93.96   $93.95   $94.00  
  Purchase #2 $24.61   4.224%   $25.6495   $25.65   $25.65   $25.60  
  Purchase #3 $139.54   13.427%   $158.276   $158.28   $158.30   $158.30  
  Purchase #4 $111.32   5.213%   $117.1231   $117.12   $117.10   $117.10  
  Purchase #5 $170.84   10.301%   $188.4382   $188.44   $188.45   $188.40  
  Purchase #6 $157.99   7.760%   $170.25   $170.25   $170.25   $170.30  
  Purchase #7 $152.44   11.731%   $170.3227   $170.32   $170.30   $170.30  
  7 purchase totals = $841.57       $924.0155   $924.02   $924.00   $924.00