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 $41.57   7.486%   $44.6819   $44.68   $44.70   $44.70  
  Purchase #2 $236.65   10.548%   $261.6118   $261.61   $261.60   $261.60  
  Purchase #3 $82.83   11.519%   $92.3712   $92.37   $92.35   $92.40  
  Purchase #4 $193.58   10.410%   $213.7317   $213.73   $213.75   $213.70  
  Purchase #5 $55.54   12.472%   $62.4669   $62.47   $62.45   $62.50  
  Purchase #6 $184.33   11.212%   $204.9971   $205.00   $205.00   $205.00  
  Purchase #7 $220.26   4.211%   $229.5351   $229.54   $229.55   $229.50  
  7 purchase totals = $1,014.76       $1,109.3957   $1,109.40   $1,109.40   $1,109.40