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 $131.82   11.458%   $146.9239   $146.92   $146.90   $146.90  
  Purchase #2 $135.94   11.271%   $151.2618   $151.26   $151.25   $151.30  
  Purchase #3 $148.47   7.765%   $159.9987   $160.00   $160.00   $160.00  
  Purchase #4 $26.77   9.446%   $29.2987   $29.30   $29.30   $29.30  
  Purchase #5 $132.47   9.263%   $144.7407   $144.74   $144.75   $144.70  
  Purchase #6 $230.41   4.520%   $240.8245   $240.82   $240.80   $240.80  
  Purchase #7 $140.55   8.623%   $152.6696   $152.67   $152.65   $152.70  
  7 purchase totals = $946.43       $1,025.7179   $1,025.71   $1,025.65   $1,025.70