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 $74.68   12.736%   $84.1912   $84.19   $84.20   $84.20  
  Purchase #2 $62.47   4.383%   $65.2081   $65.21   $65.20   $65.20  
  Purchase #3 $165.45   3.297%   $170.9049   $170.90   $170.90   $170.90  
  Purchase #4 $250.85   13.459%   $284.6119   $284.61   $284.60   $284.60  
  Purchase #5 $100.26   13.255%   $113.5495   $113.55   $113.55   $113.50  
  Purchase #6 $11.84   3.235%   $12.223   $12.22   $12.20   $12.20  
  Purchase #7 $5.79   9.781%   $6.3563   $6.36   $6.35   $6.40  
  7 purchase totals = $671.34       $737.0449   $737.04   $737.00   $737.00