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 $66.86   10.557%   $73.9184   $73.92   $73.90   $73.90  
  Purchase #2 $201.78   3.300%   $208.4387   $208.44   $208.45   $208.40  
  Purchase #3 $238.47   7.221%   $255.6899   $255.69   $255.70   $255.70  
  Purchase #4 $182.25   12.625%   $205.2591   $205.26   $205.25   $205.30  
  Purchase #5 $217.30   3.489%   $224.8816   $224.88   $224.90   $224.90  
  Purchase #6 $121.39   12.459%   $136.514   $136.51   $136.50   $136.50  
  Purchase #7 $220.65   10.117%   $242.9732   $242.97   $242.95   $243.00  
  7 purchase totals = $1,248.70       $1,347.6749   $1,347.67   $1,347.65   $1,347.70