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 $185.84   10.344%   $205.0633   $205.06   $205.05   $205.10  
  Purchase #2 $94.91   8.320%   $102.8065   $102.81   $102.80   $102.80  
  Purchase #3 $160.91   8.657%   $174.84   $174.84   $174.85   $174.80  
  Purchase #4 $32.53   3.604%   $33.7024   $33.70   $33.70   $33.70  
  Purchase #5 $224.53   13.406%   $254.6305   $254.63   $254.65   $254.60  
  Purchase #6 $163.69   11.318%   $182.2164   $182.22   $182.20   $182.20  
  Purchase #7 $109.34   8.208%   $118.3146   $118.31   $118.30   $118.30  
  7 purchase totals = $971.75       $1,071.5737   $1,071.57   $1,071.55   $1,071.50