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 $171.91   12.867%   $194.0297   $194.03   $194.05   $194.00  
  Purchase #2 $105.85   6.137%   $112.346   $112.35   $112.35   $112.30  
  Purchase #3 $144.57   9.722%   $158.6251   $158.63   $158.65   $158.60  
  Purchase #4 $240.57   5.339%   $253.414   $253.41   $253.40   $253.40  
  Purchase #5 $148.62   12.525%   $167.2347   $167.23   $167.25   $167.20  
  Purchase #6 $246.50   6.622%   $262.8232   $262.82   $262.80   $262.80  
  Purchase #7 $11.62   6.836%   $12.4143   $12.41   $12.40   $12.40  
  7 purchase totals = $1,069.64       $1,160.8870   $1,160.88   $1,160.90   $1,160.70