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 $211.73   10.549%   $234.0654   $234.07   $234.05   $234.10  
  Purchase #2 $146.87   6.233%   $156.0244   $156.02   $156.00   $156.00  
  Purchase #3 $185.35   7.204%   $198.7026   $198.70   $198.70   $198.70  
  Purchase #4 $196.82   8.275%   $213.1069   $213.11   $213.10   $213.10  
  Purchase #5 $56.84   6.172%   $60.3482   $60.35   $60.35   $60.30  
  Purchase #6 $32.96   3.254%   $34.0325   $34.03   $34.05   $34.00  
  Purchase #7 $64.41   10.433%   $71.1299   $71.13   $71.15   $71.10  
  7 purchase totals = $894.98       $967.4099   $967.41   $967.40   $967.30