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 $58.55   12.385%   $65.8014   $65.80   $65.80   $65.80  
  Purchase #2 $216.77   11.762%   $242.2665   $242.27   $242.25   $242.30  
  Purchase #3 $15.32   13.626%   $17.4075   $17.41   $17.40   $17.40  
  Purchase #4 $6.88   5.572%   $7.2634   $7.26   $7.25   $7.30  
  Purchase #5 $93.37   3.789%   $96.9078   $96.91   $96.90   $96.90  
  Purchase #6 $217.45   9.471%   $238.0447   $238.04   $238.05   $238.00  
  Purchase #7 $165.92   12.707%   $187.0035   $187.00   $187.00   $187.00  
  7 purchase totals = $774.26       $854.6948   $854.69   $854.65   $854.70