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 $89.65   7.733%   $96.5826   $96.58   $96.60   $96.60  
  Purchase #2 $151.97   5.720%   $160.6627   $160.66   $160.65   $160.70  
  Purchase #3 $31.77   4.642%   $33.2448   $33.24   $33.25   $33.20  
  Purchase #4 $220.41   3.380%   $227.8599   $227.86   $227.85   $227.90  
  Purchase #5 $125.29   7.132%   $134.2257   $134.23   $134.25   $134.20  
  Purchase #6 $27.47   4.490%   $28.7034   $28.70   $28.70   $28.70  
  Purchase #7 $191.55   7.128%   $205.2037   $205.20   $205.20   $205.20  
  7 purchase totals = $838.11       $886.4828   $886.47   $886.50   $886.50