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 $56.98   6.839%   $60.8769   $60.88   $60.90   $60.90  
  Purchase #2 $232.69   11.629%   $259.7495   $259.75   $259.75   $259.70  
  Purchase #3 $219.76   13.362%   $249.1243   $249.12   $249.10   $249.10  
  Purchase #4 $250.29   9.589%   $274.2903   $274.29   $274.30   $274.30  
  Purchase #5 $112.27   11.376%   $125.0418   $125.04   $125.05   $125.00  
  Purchase #6 $8.96   4.175%   $9.3341   $9.33   $9.35   $9.30  
  Purchase #7 $91.96   9.558%   $100.7495   $100.75   $100.75   $100.70  
  7 purchase totals = $972.91       $1,079.1664   $1,079.16   $1,079.20   $1,079.00