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 $245.41   11.655%   $274.0125   $274.01   $274.00   $274.00  
  Purchase #2 $57.69   4.854%   $60.4903   $60.49   $60.50   $60.50  
  Purchase #3 $14.73   11.218%   $16.3824   $16.38   $16.40   $16.40  
  Purchase #4 $175.47   8.242%   $189.9322   $189.93   $189.95   $189.90  
  Purchase #5 $217.65   13.119%   $246.2035   $246.20   $246.20   $246.20  
  Purchase #6 $235.61   8.829%   $256.412   $256.41   $256.40   $256.40  
  Purchase #7 $95.52   7.719%   $102.8932   $102.89   $102.90   $102.90  
  7 purchase totals = $1,042.08       $1,146.3261   $1,146.31   $1,146.35   $1,146.30