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 $244.44   4.406%   $255.21   $255.21   $255.20   $255.20  
  Purchase #2 $54.99   4.653%   $57.5487   $57.55   $57.55   $57.50  
  Purchase #3 $201.26   11.265%   $223.9319   $223.93   $223.95   $223.90  
  Purchase #4 $120.85   4.578%   $126.3825   $126.38   $126.40   $126.40  
  Purchase #5 $8.30   13.570%   $9.4263   $9.43   $9.45   $9.40  
  Purchase #6 $246.90   11.372%   $274.9775   $274.98   $275.00   $275.00  
  Purchase #7 $62.88   9.464%   $68.831   $68.83   $68.85   $68.80  
  7 purchase totals = $939.62       $1,016.3079   $1,016.31   $1,016.40   $1,016.20