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 $104.88   13.460%   $118.9968   $119.00   $119.00   $119.00  
  Purchase #2 $235.46   10.792%   $260.8708   $260.87   $260.85   $260.90  
  Purchase #3 $248.86   7.777%   $268.2138   $268.21   $268.20   $268.20  
  Purchase #4 $115.83   8.837%   $126.0659   $126.07   $126.05   $126.10  
  Purchase #5 $68.87   11.136%   $76.5394   $76.54   $76.55   $76.50  
  Purchase #6 $90.58   3.248%   $93.522   $93.52   $93.50   $93.50  
  Purchase #7 $5.49   6.412%   $5.842   $5.84   $5.85   $5.80  
  7 purchase totals = $869.97       $950.0507   $950.05   $950.00   $950.00