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 $66.95   8.754%   $72.8108   $72.81   $72.80   $72.80  
  Purchase #2 $244.80   11.468%   $272.8737   $272.87   $272.85   $272.90  
  Purchase #3 $227.65   9.234%   $248.6712   $248.67   $248.65   $248.70  
  Purchase #4 $118.64   7.797%   $127.8904   $127.89   $127.90   $127.90  
  Purchase #5 $236.99   13.273%   $268.4457   $268.45   $268.45   $268.40  
  Purchase #6 $68.32   10.801%   $75.6992   $75.70   $75.70   $75.70  
  Purchase #7 $71.25   4.265%   $74.2888   $74.29   $74.30   $74.30  
  7 purchase totals = $1,034.60       $1,140.6798   $1,140.68   $1,140.65   $1,140.70