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 $44.33   3.747%   $45.991   $45.99   $46.00   $46.00  
  Purchase #2 $104.77   8.856%   $114.0484   $114.05   $114.05   $114.00  
  Purchase #3 $125.61   8.795%   $136.6574   $136.66   $136.65   $136.70  
  Purchase #4 $233.88   7.565%   $251.573   $251.57   $251.55   $251.60  
  Purchase #5 $158.54   7.768%   $170.8554   $170.86   $170.85   $170.90  
  Purchase #6 $52.96   3.589%   $54.8607   $54.86   $54.85   $54.90  
  Purchase #7 $46.61   7.633%   $50.1677   $50.17   $50.15   $50.20  
  7 purchase totals = $766.70       $824.1536   $824.16   $824.10   $824.30