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 $37.28   11.651%   $41.6235   $41.62   $41.60   $41.60  
  Purchase #2 $132.53   13.598%   $150.5514   $150.55   $150.55   $150.60  
  Purchase #3 $177.31   5.625%   $187.2837   $187.28   $187.30   $187.30  
  Purchase #4 $5.67   11.844%   $6.3416   $6.34   $6.35   $6.30  
  Purchase #5 $150.45   10.545%   $166.315   $166.32   $166.30   $166.30  
  Purchase #6 $183.67   4.528%   $191.9866   $191.99   $192.00   $192.00  
  Purchase #7 $56.26   12.292%   $63.1755   $63.18   $63.20   $63.20  
  7 purchase totals = $743.17       $807.2773   $807.28   $807.30   $807.30