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 $188.38   13.662%   $214.1165   $214.12   $214.10   $214.10  
  Purchase #2 $217.33   4.842%   $227.8531   $227.85   $227.85   $227.90  
  Purchase #3 $94.80   7.557%   $101.964   $101.96   $101.95   $102.00  
  Purchase #4 $24.25   9.379%   $26.5244   $26.52   $26.50   $26.50  
  Purchase #5 $227.88   7.589%   $245.1738   $245.17   $245.15   $245.20  
  Purchase #6 $74.87   13.362%   $84.8741   $84.87   $84.85   $84.90  
  Purchase #7 $114.30   8.260%   $123.7412   $123.74   $123.75   $123.70  
  7 purchase totals = $941.81       $1,024.2471   $1,024.23   $1,024.15   $1,024.30