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 $176.81   13.706%   $201.0436   $201.04   $201.05   $201.00  
  Purchase #2 $17.75   7.398%   $19.0631   $19.06   $19.05   $19.10  
  Purchase #3 $243.92   5.102%   $256.3648   $256.36   $256.35   $256.40  
  Purchase #4 $84.25   6.295%   $89.5535   $89.55   $89.55   $89.60  
  Purchase #5 $5.57   8.738%   $6.0567   $6.06   $6.05   $6.10  
  Purchase #6 $24.50   3.219%   $25.2887   $25.29   $25.30   $25.30  
  Purchase #7 $75.58   10.483%   $83.5031   $83.50   $83.50   $83.50  
  7 purchase totals = $628.38       $680.8735   $680.86   $680.85   $681.00