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 $81.79   11.365%   $91.0854   $91.09   $91.10   $91.10  
  Purchase #2 $159.62   4.607%   $166.9737   $166.97   $166.95   $167.00  
  Purchase #3 $153.97   12.741%   $173.5873   $173.59   $173.60   $173.60  
  Purchase #4 $73.70   13.762%   $83.8426   $83.84   $83.85   $83.80  
  Purchase #5 $244.53   9.699%   $268.247   $268.25   $268.25   $268.20  
  Purchase #6 $21.26   8.781%   $23.1268   $23.13   $23.15   $23.10  
  Purchase #7 $184.39   12.808%   $208.0067   $208.01   $208.00   $208.00  
  7 purchase totals = $919.26       $1,014.8695   $1,014.88   $1,014.90   $1,014.80