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 $85.62   13.209%   $96.9295   $96.93   $96.95   $96.90  
  Purchase #2 $133.40   3.685%   $138.3158   $138.32   $138.30   $138.30  
  Purchase #3 $97.82   4.169%   $101.8981   $101.90   $101.90   $101.90  
  Purchase #4 $182.67   10.570%   $201.9782   $201.98   $202.00   $202.00  
  Purchase #5 $175.55   4.409%   $183.29   $183.29   $183.30   $183.30  
  Purchase #6 $199.70   4.663%   $209.012   $209.01   $209.00   $209.00  
  Purchase #7 $28.75   3.699%   $29.8135   $29.81   $29.80   $29.80  
  7 purchase totals = $903.51       $961.2371   $961.24   $961.25   $961.20