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 $87.31   12.260%   $98.0142   $98.01   $98.00   $98.00  
  Purchase #2 $193.59   12.525%   $217.8371   $217.84   $217.85   $217.80  
  Purchase #3 $206.49   8.674%   $224.4009   $224.40   $224.40   $224.40  
  Purchase #4 $118.42   8.193%   $128.1222   $128.12   $128.10   $128.10  
  Purchase #5 $91.39   7.196%   $97.9664   $97.97   $97.95   $98.00  
  Purchase #6 $242.54   11.579%   $270.6237   $270.62   $270.60   $270.60  
  Purchase #7 $183.29   13.118%   $207.334   $207.33   $207.35   $207.30  
  7 purchase totals = $1,123.03       $1,244.2985   $1,244.29   $1,244.25   $1,244.20