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 $72.89   4.234%   $75.9762   $75.98   $76.00   $76.00  
  Purchase #2 $152.57   10.737%   $168.9514   $168.95   $168.95   $169.00  
  Purchase #3 $191.85   9.487%   $210.0508   $210.05   $210.05   $210.10  
  Purchase #4 $49.56   12.761%   $55.8844   $55.88   $55.90   $55.90  
  Purchase #5 $173.51   9.234%   $189.5319   $189.53   $189.55   $189.50  
  Purchase #6 $240.70   6.311%   $255.8906   $255.89   $255.90   $255.90  
  Purchase #7 $179.51   12.532%   $202.0062   $202.01   $202.00   $202.00  
  7 purchase totals = $1,060.59       $1,158.2915   $1,158.29   $1,158.35   $1,158.40