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 $51.76   11.784%   $57.8594   $57.86   $57.85   $57.90  
  Purchase #2 $161.56   13.270%   $182.999   $183.00   $183.00   $183.00  
  Purchase #3 $96.86   11.410%   $107.9117   $107.91   $107.90   $107.90  
  Purchase #4 $26.79   3.418%   $27.7057   $27.71   $27.70   $27.70  
  Purchase #5 $163.31   5.139%   $171.7025   $171.70   $171.70   $171.70  
  Purchase #6 $64.47   13.781%   $73.3546   $73.35   $73.35   $73.40  
  Purchase #7 $248.44   10.302%   $274.0343   $274.03   $274.05   $274.00  
  7 purchase totals = $813.19       $895.5672   $895.56   $895.55   $895.60