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 $56.91   13.453%   $64.5661   $64.57   $64.55   $64.60  
  Purchase #2 $241.96   4.469%   $252.7732   $252.77   $252.75   $252.80  
  Purchase #3 $46.70   6.365%   $49.6725   $49.67   $49.65   $49.70  
  Purchase #4 $123.89   6.313%   $131.7112   $131.71   $131.70   $131.70  
  Purchase #5 $20.40   13.289%   $23.111   $23.11   $23.10   $23.10  
  Purchase #6 $64.36   7.179%   $68.9804   $68.98   $69.00   $69.00  
  Purchase #7 $148.32   12.427%   $166.7517   $166.75   $166.75   $166.80  
  7 purchase totals = $702.54       $757.5661   $757.56   $757.50   $757.70