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 $239.59   10.727%   $265.2908   $265.29   $265.30   $265.30  
  Purchase #2 $55.61   8.448%   $60.3079   $60.31   $60.30   $60.30  
  Purchase #3 $8.52   8.814%   $9.271   $9.27   $9.25   $9.30  
  Purchase #4 $99.53   6.838%   $106.3359   $106.34   $106.35   $106.30  
  Purchase #5 $159.61   4.696%   $167.1053   $167.11   $167.10   $167.10  
  Purchase #6 $154.67   11.768%   $172.8716   $172.87   $172.85   $172.90  
  Purchase #7 $81.70   11.697%   $91.2564   $91.26   $91.25   $91.30  
  7 purchase totals = $799.23       $872.4389   $872.45   $872.40   $872.50