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 $58.32   11.221%   $64.8641   $64.86   $64.85   $64.90  
  Purchase #2 $164.49   6.575%   $175.3052   $175.31   $175.30   $175.30  
  Purchase #3 $200.96   8.565%   $218.1722   $218.17   $218.15   $218.20  
  Purchase #4 $123.95   7.276%   $132.9686   $132.97   $132.95   $133.00  
  Purchase #5 $220.59   13.331%   $249.9969   $250.00   $250.00   $250.00  
  Purchase #6 $8.34   12.344%   $9.3695   $9.37   $9.35   $9.40  
  Purchase #7 $240.98   11.436%   $268.5385   $268.54   $268.55   $268.50  
  7 purchase totals = $1,017.63       $1,119.2150   $1,119.22   $1,119.15   $1,119.30