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 $39.60   9.396%   $43.3208   $43.32   $43.30   $43.30  
  Purchase #2 $141.56   10.403%   $156.2865   $156.29   $156.30   $156.30  
  Purchase #3 $62.37   7.215%   $66.87   $66.87   $66.85   $66.90  
  Purchase #4 $151.67   9.600%   $166.2303   $166.23   $166.25   $166.20  
  Purchase #5 $12.43   12.552%   $13.9902   $13.99   $14.00   $14.00  
  Purchase #6 $245.76   6.734%   $262.3095   $262.31   $262.30   $262.30  
  Purchase #7 $70.36   8.436%   $76.2956   $76.30   $76.30   $76.30  
  7 purchase totals = $723.75       $785.3029   $785.31   $785.30   $785.30