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 $55.70   11.379%   $62.0381   $62.04   $62.05   $62.00  
  Purchase #2 $16.28   9.842%   $17.8823   $17.88   $17.90   $17.90  
  Purchase #3 $132.89   3.121%   $137.0375   $137.04   $137.05   $137.00  
  Purchase #4 $74.37   4.451%   $77.6802   $77.68   $77.70   $77.70  
  Purchase #5 $229.80   5.235%   $241.83   $241.83   $241.85   $241.80  
  Purchase #6 $94.75   5.374%   $99.8419   $99.84   $99.85   $99.80  
  Purchase #7 $18.78   8.611%   $20.3971   $20.40   $20.40   $20.40  
  7 purchase totals = $622.57       $656.7071   $656.71   $656.80   $656.60