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 $14.32   6.556%   $15.2588   $15.26   $15.25   $15.30  
  Purchase #2 $92.68   13.655%   $105.3355   $105.34   $105.35   $105.30  
  Purchase #3 $230.27   7.282%   $247.0383   $247.04   $247.05   $247.00  
  Purchase #4 $150.92   8.617%   $163.9248   $163.92   $163.90   $163.90  
  Purchase #5 $198.32   7.327%   $212.8509   $212.85   $212.85   $212.90  
  Purchase #6 $52.67   3.433%   $54.4782   $54.48   $54.50   $54.50  
  Purchase #7 $231.56   10.103%   $254.9545   $254.95   $254.95   $255.00  
  7 purchase totals = $970.74       $1,053.8410   $1,053.84   $1,053.85   $1,053.90