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 $167.63   3.498%   $173.4937   $173.49   $173.50   $173.50  
  Purchase #2 $210.73   4.806%   $220.8577   $220.86   $220.85   $220.90  
  Purchase #3 $246.39   3.814%   $255.7873   $255.79   $255.80   $255.80  
  Purchase #4 $138.32   7.353%   $148.4907   $148.49   $148.50   $148.50  
  Purchase #5 $85.77   9.571%   $93.979   $93.98   $94.00   $94.00  
  Purchase #6 $206.71   5.442%   $217.9592   $217.96   $217.95   $218.00  
  Purchase #7 $239.75   3.722%   $248.6735   $248.67   $248.65   $248.70  
  7 purchase totals = $1,295.30       $1,359.2411   $1,359.24   $1,359.25   $1,359.40