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 $95.73   9.282%   $104.6157   $104.62   $104.60   $104.60  
  Purchase #2 $99.78   10.607%   $110.3637   $110.36   $110.35   $110.40  
  Purchase #3 $51.73   5.358%   $54.5017   $54.50   $54.50   $54.50  
  Purchase #4 $55.41   13.122%   $62.6809   $62.68   $62.70   $62.70  
  Purchase #5 $177.83   10.805%   $197.0445   $197.04   $197.05   $197.00  
  Purchase #6 $35.37   10.241%   $38.9922   $38.99   $39.00   $39.00  
  Purchase #7 $165.68   5.513%   $174.8139   $174.81   $174.80   $174.80  
  7 purchase totals = $681.53       $743.0126   $743.00   $743.00   $743.00