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 $23.71   13.214%   $26.843   $26.84   $26.85   $26.80  
  Purchase #2 $109.33   4.230%   $113.9547   $113.95   $113.95   $114.00  
  Purchase #3 $212.53   11.743%   $237.4874   $237.49   $237.50   $237.50  
  Purchase #4 $247.33   4.691%   $258.9323   $258.93   $258.95   $258.90  
  Purchase #5 $19.53   8.556%   $21.201   $21.20   $21.20   $21.20  
  Purchase #6 $244.28   8.449%   $264.9192   $264.92   $264.90   $264.90  
  Purchase #7 $185.52   5.224%   $195.2116   $195.21   $195.20   $195.20  
  7 purchase totals = $1,042.23       $1,118.5492   $1,118.54   $1,118.55   $1,118.50