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 $60.83   6.561%   $64.8211   $64.82   $64.80   $64.80  
  Purchase #2 $204.90   5.510%   $216.19   $216.19   $216.20   $216.20  
  Purchase #3 $18.71   6.125%   $19.856   $19.86   $19.85   $19.90  
  Purchase #4 $39.54   12.472%   $44.4714   $44.47   $44.45   $44.50  
  Purchase #5 $204.44   11.158%   $227.2514   $227.25   $227.25   $227.30  
  Purchase #6 $116.31   11.471%   $129.6519   $129.65   $129.65   $129.70  
  Purchase #7 $249.55   5.773%   $263.9565   $263.96   $263.95   $264.00  
  7 purchase totals = $894.28       $966.1983   $966.20   $966.15   $966.40