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 $41.94   11.307%   $46.6822   $46.68   $46.70   $46.70  
  Purchase #2 $86.85   8.270%   $94.0325   $94.03   $94.05   $94.00  
  Purchase #3 $159.49   8.185%   $172.5443   $172.54   $172.55   $172.50  
  Purchase #4 $104.85   3.548%   $108.5701   $108.57   $108.55   $108.60  
  Purchase #5 $25.53   5.734%   $26.9939   $26.99   $27.00   $27.00  
  Purchase #6 $149.25   6.834%   $159.4497   $159.45   $159.45   $159.40  
  Purchase #7 $155.56   10.682%   $172.1769   $172.18   $172.20   $172.20  
  7 purchase totals = $723.47       $780.4496   $780.44   $780.50   $780.40