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 $39.50   5.270%   $41.5817   $41.58   $41.60   $41.60  
  Purchase #2 $182.91   4.766%   $191.6275   $191.63   $191.65   $191.60  
  Purchase #3 $70.67   6.551%   $75.2996   $75.30   $75.30   $75.30  
  Purchase #4 $155.35   7.259%   $166.6269   $166.63   $166.65   $166.60  
  Purchase #5 $236.31   13.506%   $268.226   $268.23   $268.25   $268.20  
  Purchase #6 $63.25   12.388%   $71.0854   $71.09   $71.10   $71.10  
  Purchase #7 $135.74   10.870%   $150.4949   $150.49   $150.50   $150.50  
  7 purchase totals = $883.73       $964.9420   $964.95   $965.05   $964.90