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 $32.60   4.841%   $34.1782   $34.18   $34.20   $34.20  
  Purchase #2 $191.94   3.852%   $199.3335   $199.33   $199.35   $199.30  
  Purchase #3 $226.78   9.247%   $247.7503   $247.75   $247.75   $247.80  
  Purchase #4 $191.33   5.507%   $201.8665   $201.87   $201.85   $201.90  
  Purchase #5 $197.25   5.518%   $208.1343   $208.13   $208.15   $208.10  
  Purchase #6 $61.57   6.228%   $65.4046   $65.40   $65.40   $65.40  
  Purchase #7 $28.38   3.830%   $29.467   $29.47   $29.45   $29.50  
  7 purchase totals = $929.85       $986.1344   $986.13   $986.15   $986.20