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 $91.54   7.224%   $98.1528   $98.15   $98.15   $98.20  
  Purchase #2 $217.45   12.834%   $245.3575   $245.36   $245.35   $245.40  
  Purchase #3 $233.76   7.466%   $251.2125   $251.21   $251.20   $251.20  
  Purchase #4 $107.40   9.311%   $117.4   $117.40   $117.40   $117.40  
  Purchase #5 $82.58   4.840%   $86.5769   $86.58   $86.60   $86.60  
  Purchase #6 $30.49   9.279%   $33.3192   $33.32   $33.30   $33.30  
  Purchase #7 $197.71   11.672%   $220.7867   $220.79   $220.80   $220.80  
  7 purchase totals = $960.93       $1,052.8056   $1,052.81   $1,052.80   $1,052.90