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 $123.39   5.514%   $130.1937   $130.19   $130.20   $130.20  
  Purchase #2 $142.96   9.351%   $156.3282   $156.33   $156.35   $156.30  
  Purchase #3 $192.60   3.763%   $199.8475   $199.85   $199.85   $199.80  
  Purchase #4 $148.45   8.836%   $161.567   $161.57   $161.55   $161.60  
  Purchase #5 $245.51   5.424%   $258.8265   $258.83   $258.85   $258.80  
  Purchase #6 $116.91   12.503%   $131.5273   $131.53   $131.55   $131.50  
  Purchase #7 $170.73   3.219%   $176.2258   $176.23   $176.25   $176.20  
  7 purchase totals = $1,140.55       $1,214.5160   $1,214.53   $1,214.60   $1,214.40