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 $64.74   13.319%   $73.3627   $73.36   $73.35   $73.40  
  Purchase #2 $131.68   12.244%   $147.8029   $147.80   $147.80   $147.80  
  Purchase #3 $168.94   10.378%   $186.4726   $186.47   $186.45   $186.50  
  Purchase #4 $213.34   8.818%   $232.1523   $232.15   $232.15   $232.20  
  Purchase #5 $59.54   13.165%   $67.3784   $67.38   $67.40   $67.40  
  Purchase #6 $202.40   13.647%   $230.0215   $230.02   $230.00   $230.00  
  Purchase #7 $13.98   12.689%   $15.7539   $15.75   $15.75   $15.80  
  7 purchase totals = $854.62       $952.9443   $952.93   $952.90   $953.10