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 $97.37   13.561%   $110.5743   $110.57   $110.55   $110.60  
  Purchase #2 $164.31   8.624%   $178.4801   $178.48   $178.50   $178.50  
  Purchase #3 $118.46   4.836%   $124.1887   $124.19   $124.20   $124.20  
  Purchase #4 $136.39   13.290%   $154.5162   $154.52   $154.50   $154.50  
  Purchase #5 $151.79   5.566%   $160.2386   $160.24   $160.25   $160.20  
  Purchase #6 $209.72   6.727%   $223.8279   $223.83   $223.85   $223.80  
  Purchase #7 $156.90   11.644%   $175.1694   $175.17   $175.15   $175.20  
  7 purchase totals = $1,034.94       $1,126.9952   $1,127.00   $1,127.00   $1,127.00