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 $248.95   6.397%   $264.8753   $264.88   $264.90   $264.90  
  Purchase #2 $189.63   13.127%   $214.5227   $214.52   $214.50   $214.50  
  Purchase #3 $62.40   6.125%   $66.222   $66.22   $66.20   $66.20  
  Purchase #4 $122.99   7.752%   $132.5242   $132.52   $132.50   $132.50  
  Purchase #5 $177.79   4.443%   $185.6892   $185.69   $185.70   $185.70  
  Purchase #6 $91.47   3.106%   $94.3111   $94.31   $94.30   $94.30  
  Purchase #7 $49.96   12.654%   $56.2819   $56.28   $56.30   $56.30  
  7 purchase totals = $943.19       $1,014.4264   $1,014.42   $1,014.40   $1,014.40