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 $98.86   6.114%   $104.9043   $104.90   $104.90   $104.90  
  Purchase #2 $169.33   9.463%   $185.3537   $185.35   $185.35   $185.40  
  Purchase #3 $209.27   11.459%   $233.2502   $233.25   $233.25   $233.30  
  Purchase #4 $53.99   8.571%   $58.6175   $58.62   $58.60   $58.60  
  Purchase #5 $33.31   6.172%   $35.3659   $35.37   $35.35   $35.40  
  Purchase #6 $234.91   10.656%   $259.942   $259.94   $259.95   $259.90  
  Purchase #7 $110.27   4.807%   $115.5707   $115.57   $115.55   $115.60  
  7 purchase totals = $909.94       $993.0043   $993.00   $992.95   $993.10