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 $178.83   7.266%   $191.8238   $191.82   $191.80   $191.80  
  Purchase #2 $147.80   7.281%   $158.5613   $158.56   $158.55   $158.60  
  Purchase #3 $102.76   7.646%   $110.617   $110.62   $110.60   $110.60  
  Purchase #4 $146.71   11.567%   $163.6799   $163.68   $163.70   $163.70  
  Purchase #5 $150.69   10.179%   $166.0287   $166.03   $166.05   $166.00  
  Purchase #6 $84.94   10.187%   $93.5928   $93.59   $93.60   $93.60  
  Purchase #7 $165.78   5.379%   $174.6973   $174.70   $174.70   $174.70  
  7 purchase totals = $977.51       $1,059.0008   $1,059.00   $1,059.00   $1,059.00