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 $46.60   8.775%   $50.6892   $50.69   $50.70   $50.70  
  Purchase #2 $205.31   5.140%   $215.8629   $215.86   $215.85   $215.90  
  Purchase #3 $141.86   4.232%   $147.8635   $147.86   $147.85   $147.90  
  Purchase #4 $5.95   11.499%   $6.6342   $6.63   $6.65   $6.60  
  Purchase #5 $148.33   4.150%   $154.4857   $154.49   $154.50   $154.50  
  Purchase #6 $237.25   5.374%   $249.9998   $250.00   $250.00   $250.00  
  Purchase #7 $9.26   12.675%   $10.4337   $10.43   $10.45   $10.40  
  7 purchase totals = $794.56       $835.9690   $835.96   $836.00   $836.00