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 $62.42   12.654%   $70.3186   $70.32   $70.30   $70.30  
  Purchase #2 $248.73   13.355%   $281.9479   $281.95   $281.95   $281.90  
  Purchase #3 $17.80   7.779%   $19.1847   $19.18   $19.20   $19.20  
  Purchase #4 $233.46   11.335%   $259.9227   $259.92   $259.90   $259.90  
  Purchase #5 $245.30   5.281%   $258.2543   $258.25   $258.25   $258.30  
  Purchase #6 $9.40   5.490%   $9.9161   $9.92   $9.90   $9.90  
  Purchase #7 $232.84   7.162%   $249.516   $249.52   $249.50   $249.50  
  7 purchase totals = $1,049.95       $1,149.0603   $1,149.06   $1,149.00   $1,149.00