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 $141.61   7.260%   $151.8909   $151.89   $151.90   $151.90  
  Purchase #2 $249.58   5.426%   $263.1222   $263.12   $263.10   $263.10  
  Purchase #3 $221.43   8.402%   $240.0345   $240.03   $240.05   $240.00  
  Purchase #4 $188.98   4.650%   $197.7676   $197.77   $197.75   $197.80  
  Purchase #5 $75.31   3.143%   $77.677   $77.68   $77.70   $77.70  
  Purchase #6 $55.61   12.268%   $62.4322   $62.43   $62.45   $62.40  
  Purchase #7 $25.53   12.252%   $28.6579   $28.66   $28.65   $28.70  
  7 purchase totals = $958.05       $1,021.5823   $1,021.58   $1,021.60   $1,021.60