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 $52.26   8.777%   $56.8469   $56.85   $56.85   $56.80  
  Purchase #2 $49.85   12.873%   $56.2672   $56.27   $56.25   $56.30  
  Purchase #3 $60.72   3.642%   $62.9314   $62.93   $62.95   $62.90  
  Purchase #4 $28.95   10.463%   $31.979   $31.98   $32.00   $32.00  
  Purchase #5 $18.42   5.180%   $19.3742   $19.37   $19.35   $19.40  
  Purchase #6 $250.74   3.752%   $260.1478   $260.15   $260.15   $260.10  
  Purchase #7 $156.36   6.773%   $166.9503   $166.95   $166.95   $167.00  
  7 purchase totals = $617.30       $654.4968   $654.50   $654.50   $654.50