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 $170.54   7.294%   $182.9792   $182.98   $183.00   $183.00  
  Purchase #2 $154.42   4.249%   $160.9813   $160.98   $161.00   $161.00  
  Purchase #3 $47.60   8.203%   $51.5046   $51.50   $51.50   $51.50  
  Purchase #4 $44.75   11.214%   $49.7683   $49.77   $49.75   $49.80  
  Purchase #5 $116.34   3.628%   $120.5608   $120.56   $120.55   $120.60  
  Purchase #6 $110.58   7.426%   $118.7917   $118.79   $118.80   $118.80  
  Purchase #7 $247.30   11.819%   $276.5284   $276.53   $276.55   $276.50  
  7 purchase totals = $891.53       $961.1143   $961.11   $961.15   $961.20