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 $64.87   6.354%   $68.9918   $68.99   $69.00   $69.00  
  Purchase #2 $231.54   13.604%   $263.0387   $263.04   $263.05   $263.00  
  Purchase #3 $16.70   10.338%   $18.4264   $18.43   $18.45   $18.40  
  Purchase #4 $214.28   6.106%   $227.3639   $227.36   $227.35   $227.40  
  Purchase #5 $15.80   4.424%   $16.499   $16.50   $16.50   $16.50  
  Purchase #6 $66.71   12.323%   $74.9307   $74.93   $74.95   $74.90  
  Purchase #7 $96.86   7.562%   $104.1846   $104.18   $104.20   $104.20  
  7 purchase totals = $706.76       $773.4351   $773.43   $773.50   $773.40