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 $232.26   11.173%   $258.2104   $258.21   $258.20   $258.20  
  Purchase #2 $195.87   7.181%   $209.9354   $209.94   $209.95   $209.90  
  Purchase #3 $67.45   11.336%   $75.0961   $75.10   $75.10   $75.10  
  Purchase #4 $60.57   9.523%   $66.3381   $66.34   $66.35   $66.30  
  Purchase #5 $94.88   4.126%   $98.7947   $98.79   $98.80   $98.80  
  Purchase #6 $94.53   6.511%   $100.6848   $100.68   $100.70   $100.70  
  Purchase #7 $156.78   11.479%   $174.7768   $174.78   $174.80   $174.80  
  7 purchase totals = $902.34       $983.8363   $983.84   $983.90   $983.80