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 $220.46   6.229%   $234.1925   $234.19   $234.20   $234.20  
  Purchase #2 $236.51   9.574%   $259.1535   $259.15   $259.15   $259.20  
  Purchase #3 $91.86   3.335%   $94.9235   $94.92   $94.90   $94.90  
  Purchase #4 $150.40   5.314%   $158.3923   $158.39   $158.40   $158.40  
  Purchase #5 $76.56   4.328%   $79.8735   $79.87   $79.85   $79.90  
  Purchase #6 $191.86   3.693%   $198.9454   $198.95   $198.95   $198.90  
  Purchase #7 $11.56   5.457%   $12.1908   $12.19   $12.20   $12.20  
  7 purchase totals = $979.21       $1,037.6715   $1,037.66   $1,037.65   $1,037.70