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 $118.61   6.390%   $126.1892   $126.19   $126.20   $126.20  
  Purchase #2 $16.85   12.498%   $18.9559   $18.96   $18.95   $19.00  
  Purchase #3 $116.88   4.800%   $122.4902   $122.49   $122.50   $122.50  
  Purchase #4 $113.43   6.249%   $120.5182   $120.52   $120.50   $120.50  
  Purchase #5 $234.61   9.549%   $257.0129   $257.01   $257.00   $257.00  
  Purchase #6 $186.93   13.414%   $212.0048   $212.00   $212.00   $212.00  
  Purchase #7 $136.41   13.396%   $154.6835   $154.68   $154.70   $154.70  
  7 purchase totals = $923.72       $1,011.8547   $1,011.85   $1,011.85   $1,011.90