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 $241.87   8.652%   $262.7966   $262.80   $262.80   $262.80  
  Purchase #2 $92.61   11.430%   $103.1953   $103.20   $103.20   $103.20  
  Purchase #3 $40.88   12.378%   $45.9401   $45.94   $45.95   $45.90  
  Purchase #4 $165.29   4.442%   $172.6322   $172.63   $172.65   $172.60  
  Purchase #5 $127.41   5.304%   $134.1678   $134.17   $134.15   $134.20  
  Purchase #6 $87.31   12.128%   $97.899   $97.90   $97.90   $97.90  
  Purchase #7 $107.89   8.851%   $117.4393   $117.44   $117.45   $117.40  
  7 purchase totals = $863.26       $934.0703   $934.08   $934.10   $934.00