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 $23.87   12.838%   $26.9344   $26.93   $26.95   $26.90  
  Purchase #2 $214.50   6.279%   $227.9685   $227.97   $227.95   $228.00  
  Purchase #3 $137.93   10.746%   $152.752   $152.75   $152.75   $152.80  
  Purchase #4 $202.50   10.323%   $223.4041   $223.40   $223.40   $223.40  
  Purchase #5 $166.25   4.339%   $173.4636   $173.46   $173.45   $173.50  
  Purchase #6 $15.76   7.647%   $16.9652   $16.97   $16.95   $17.00  
  Purchase #7 $194.62   3.675%   $201.7723   $201.77   $201.75   $201.80  
  7 purchase totals = $955.43       $1,023.2601   $1,023.25   $1,023.20   $1,023.40