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 $202.63   9.363%   $221.6022   $221.60   $221.60   $221.60  
  Purchase #2 $177.50   6.279%   $188.6452   $188.65   $188.65   $188.60  
  Purchase #3 $193.29   7.369%   $207.5335   $207.53   $207.55   $207.50  
  Purchase #4 $85.87   10.192%   $94.6219   $94.62   $94.60   $94.60  
  Purchase #5 $126.99   12.149%   $142.418   $142.42   $142.40   $142.40  
  Purchase #6 $84.30   11.293%   $93.82   $93.82   $93.80   $93.80  
  Purchase #7 $250.66   4.127%   $261.0047   $261.00   $261.00   $261.00  
  7 purchase totals = $1,121.24       $1,209.6455   $1,209.64   $1,209.60   $1,209.50