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 $243.31   11.807%   $272.0376   $272.04   $272.05   $272.00  
  Purchase #2 $151.40   10.265%   $166.9412   $166.94   $166.95   $166.90  
  Purchase #3 $14.41   9.201%   $15.7359   $15.74   $15.75   $15.70  
  Purchase #4 $62.48   9.700%   $68.5406   $68.54   $68.55   $68.50  
  Purchase #5 $187.87   12.260%   $210.9029   $210.90   $210.90   $210.90  
  Purchase #6 $208.81   11.202%   $232.2009   $232.20   $232.20   $232.20  
  Purchase #7 $87.96   5.160%   $92.4987   $92.50   $92.50   $92.50  
  7 purchase totals = $956.24       $1,058.8578   $1,058.86   $1,058.90   $1,058.70