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 $102.81   13.590%   $116.7819   $116.78   $116.80   $116.80  
  Purchase #2 $213.69   3.556%   $221.2888   $221.29   $221.30   $221.30  
  Purchase #3 $89.87   5.150%   $94.4983   $94.50   $94.50   $94.50  
  Purchase #4 $206.53   5.360%   $217.6   $217.60   $217.60   $217.60  
  Purchase #5 $56.64   10.579%   $62.6319   $62.63   $62.65   $62.60  
  Purchase #6 $230.75   8.241%   $249.7661   $249.77   $249.75   $249.80  
  Purchase #7 $60.52   6.432%   $64.4126   $64.41   $64.40   $64.40  
  7 purchase totals = $960.81       $1,026.9796   $1,026.98   $1,027.00   $1,027.00