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 $143.30   10.782%   $158.7506   $158.75   $158.75   $158.80  
  Purchase #2 $24.93   8.509%   $27.0513   $27.05   $27.05   $27.10  
  Purchase #3 $161.96   3.426%   $167.5087   $167.51   $167.50   $167.50  
  Purchase #4 $90.75   8.529%   $98.4901   $98.49   $98.50   $98.50  
  Purchase #5 $220.27   11.596%   $245.8125   $245.81   $245.80   $245.80  
  Purchase #6 $148.54   7.375%   $159.4948   $159.49   $159.50   $159.50  
  Purchase #7 $164.78   6.185%   $174.9716   $174.97   $174.95   $175.00  
  7 purchase totals = $954.53       $1,032.0796   $1,032.07   $1,032.05   $1,032.20