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 $193.26   4.617%   $202.1828   $202.18   $202.20   $202.20  
  Purchase #2 $151.42   11.362%   $168.6243   $168.62   $168.60   $168.60  
  Purchase #3 $23.44   12.258%   $26.3133   $26.31   $26.30   $26.30  
  Purchase #4 $186.52   10.867%   $206.7891   $206.79   $206.80   $206.80  
  Purchase #5 $62.99   12.756%   $71.025   $71.03   $71.05   $71.00  
  Purchase #6 $158.54   7.572%   $170.5446   $170.54   $170.55   $170.50  
  Purchase #7 $19.73   5.337%   $20.783   $20.78   $20.80   $20.80  
  7 purchase totals = $795.90       $866.2621   $866.25   $866.30   $866.20