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 $146.38   5.570%   $154.5334   $154.53   $154.55   $154.50  
  Purchase #2 $58.57   9.605%   $64.1956   $64.20   $64.20   $64.20  
  Purchase #3 $151.69   5.431%   $159.9283   $159.93   $159.95   $159.90  
  Purchase #4 $245.82   9.427%   $268.9935   $268.99   $269.00   $269.00  
  Purchase #5 $199.86   4.210%   $208.2741   $208.27   $208.25   $208.30  
  Purchase #6 $28.72   11.436%   $32.0044   $32.00   $32.00   $32.00  
  Purchase #7 $49.99   5.861%   $52.9199   $52.92   $52.90   $52.90  
  7 purchase totals = $881.03       $940.8492   $940.84   $940.85   $940.80