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 $61.26   13.218%   $69.3573   $69.36   $69.35   $69.40  
  Purchase #2 $238.27   10.493%   $263.2717   $263.27   $263.25   $263.30  
  Purchase #3 $95.49   9.530%   $104.5902   $104.59   $104.60   $104.60  
  Purchase #4 $161.49   4.570%   $168.8701   $168.87   $168.85   $168.90  
  Purchase #5 $219.76   6.618%   $234.3037   $234.30   $234.30   $234.30  
  Purchase #6 $5.68   5.192%   $5.9749   $5.97   $5.95   $6.00  
  Purchase #7 $77.58   8.136%   $83.8919   $83.89   $83.90   $83.90  
  7 purchase totals = $859.53       $930.2598   $930.25   $930.20   $930.40