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 $92.42   5.712%   $97.699   $97.70   $97.70   $97.70  
  Purchase #2 $62.60   4.602%   $65.4809   $65.48   $65.50   $65.50  
  Purchase #3 $125.57   5.758%   $132.8003   $132.80   $132.80   $132.80  
  Purchase #4 $166.94   6.378%   $177.5874   $177.59   $177.60   $177.60  
  Purchase #5 $134.86   8.326%   $146.0884   $146.09   $146.10   $146.10  
  Purchase #6 $35.61   8.523%   $38.645   $38.65   $38.65   $38.60  
  Purchase #7 $177.65   9.104%   $193.8233   $193.82   $193.80   $193.80  
  7 purchase totals = $795.65       $852.1243   $852.13   $852.15   $852.10