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 $193.75   6.485%   $206.3147   $206.31   $206.30   $206.30  
  Purchase #2 $33.87   5.431%   $35.7095   $35.71   $35.70   $35.70  
  Purchase #3 $243.75   9.339%   $266.5138   $266.51   $266.50   $266.50  
  Purchase #4 $148.70   10.223%   $163.9016   $163.90   $163.90   $163.90  
  Purchase #5 $206.28   7.533%   $221.8191   $221.82   $221.80   $221.80  
  Purchase #6 $5.27   3.789%   $5.4697   $5.47   $5.45   $5.50  
  Purchase #7 $183.66   11.630%   $205.0197   $205.02   $205.00   $205.00  
  7 purchase totals = $1,015.28       $1,104.7481   $1,104.74   $1,104.65   $1,104.70