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 $57.82   12.423%   $65.003   $65.00   $65.00   $65.00  
  Purchase #2 $169.53   4.607%   $177.3402   $177.34   $177.35   $177.30  
  Purchase #3 $11.34   3.181%   $11.7007   $11.70   $11.70   $11.70  
  Purchase #4 $90.94   7.870%   $98.097   $98.10   $98.10   $98.10  
  Purchase #5 $229.88   13.382%   $260.6425   $260.64   $260.65   $260.60  
  Purchase #6 $9.96   6.738%   $10.6311   $10.63   $10.65   $10.60  
  Purchase #7 $207.50   6.380%   $220.7385   $220.74   $220.75   $220.70  
  7 purchase totals = $776.97       $844.1530   $844.15   $844.20   $844.00