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 $32.79   12.732%   $36.9648   $36.96   $36.95   $37.00  
  Purchase #2 $234.97   8.606%   $255.1915   $255.19   $255.20   $255.20  
  Purchase #3 $20.67   12.217%   $23.1953   $23.20   $23.20   $23.20  
  Purchase #4 $46.90   5.622%   $49.5367   $49.54   $49.55   $49.50  
  Purchase #5 $239.39   5.846%   $253.3847   $253.38   $253.40   $253.40  
  Purchase #6 $45.55   11.706%   $50.8821   $50.88   $50.90   $50.90  
  Purchase #7 $230.47   3.610%   $238.79   $238.79   $238.80   $238.80  
  7 purchase totals = $850.74       $907.9451   $907.94   $908.00   $908.00