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 $23.81   12.261%   $26.7293   $26.73   $26.75   $26.70  
  Purchase #2 $211.79   9.715%   $232.3654   $232.37   $232.35   $232.40  
  Purchase #3 $141.29   9.431%   $154.6151   $154.62   $154.60   $154.60  
  Purchase #4 $77.35   9.581%   $84.7609   $84.76   $84.75   $84.80  
  Purchase #5 $147.37   11.696%   $164.6064   $164.61   $164.60   $164.60  
  Purchase #6 $233.32   10.391%   $257.5643   $257.56   $257.55   $257.60  
  Purchase #7 $23.58   4.648%   $24.676   $24.68   $24.70   $24.70  
  7 purchase totals = $858.51       $945.3174   $945.33   $945.30   $945.40