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 $14.94   12.142%   $16.754   $16.75   $16.75   $16.80  
  Purchase #2 $215.35   12.228%   $241.683   $241.68   $241.70   $241.70  
  Purchase #3 $41.62   8.489%   $45.1531   $45.15   $45.15   $45.20  
  Purchase #4 $128.59   11.262%   $143.0718   $143.07   $143.05   $143.10  
  Purchase #5 $224.60   10.384%   $247.9225   $247.92   $247.90   $247.90  
  Purchase #6 $8.72   12.366%   $9.7983   $9.80   $9.80   $9.80  
  Purchase #7 $55.88   5.141%   $58.7528   $58.75   $58.75   $58.80  
  7 purchase totals = $689.70       $763.1355   $763.12   $763.10   $763.30