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 $194.79   11.138%   $216.4857   $216.49   $216.50   $216.50  
  Purchase #2 $248.82   4.230%   $259.3451   $259.35   $259.35   $259.30  
  Purchase #3 $121.72   12.684%   $137.159   $137.16   $137.15   $137.20  
  Purchase #4 $195.66   4.579%   $204.6193   $204.62   $204.60   $204.60  
  Purchase #5 $224.93   4.254%   $234.4985   $234.50   $234.50   $234.50  
  Purchase #6 $227.30   10.519%   $251.2097   $251.21   $251.20   $251.20  
  Purchase #7 $58.25   4.609%   $60.9347   $60.93   $60.95   $60.90  
  7 purchase totals = $1,271.47       $1,364.2520   $1,364.26   $1,364.25   $1,364.20