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 $119.99   12.520%   $135.0127   $135.01   $135.00   $135.00  
  Purchase #2 $208.80   12.552%   $235.0086   $235.01   $235.00   $235.00  
  Purchase #3 $154.74   8.811%   $168.3741   $168.37   $168.35   $168.40  
  Purchase #4 $138.46   11.134%   $153.8761   $153.88   $153.90   $153.90  
  Purchase #5 $238.32   11.430%   $265.56   $265.56   $265.55   $265.60  
  Purchase #6 $170.33   5.179%   $179.1514   $179.15   $179.15   $179.20  
  Purchase #7 $119.34   4.813%   $125.0838   $125.08   $125.10   $125.10  
  7 purchase totals = $1,149.98       $1,262.0667   $1,262.06   $1,262.05   $1,262.20