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 $100.49   7.343%   $107.869   $107.87   $107.85   $107.90  
  Purchase #2 $79.62   12.172%   $89.3113   $89.31   $89.30   $89.30  
  Purchase #3 $66.98   9.743%   $73.5059   $73.51   $73.50   $73.50  
  Purchase #4 $57.98   10.381%   $63.9989   $64.00   $64.00   $64.00  
  Purchase #5 $62.30   12.511%   $70.0944   $70.09   $70.10   $70.10  
  Purchase #6 $64.47   8.511%   $69.957   $69.96   $69.95   $70.00  
  Purchase #7 $163.63   9.377%   $178.9736   $178.97   $178.95   $179.00  
  7 purchase totals = $595.47       $653.7101   $653.71   $653.65   $653.80