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 $94.48   4.363%   $98.6022   $98.60   $98.60   $98.60  
  Purchase #2 $225.64   8.116%   $243.9529   $243.95   $243.95   $244.00  
  Purchase #3 $88.34   7.335%   $94.8197   $94.82   $94.80   $94.80  
  Purchase #4 $63.51   6.451%   $67.607   $67.61   $67.60   $67.60  
  Purchase #5 $126.41   4.509%   $132.1098   $132.11   $132.10   $132.10  
  Purchase #6 $87.73   13.141%   $99.2586   $99.26   $99.25   $99.30  
  Purchase #7 $189.69   4.154%   $197.5697   $197.57   $197.55   $197.60  
  7 purchase totals = $875.80       $933.9199   $933.92   $933.85   $934.00