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 $166.52   10.599%   $184.1695   $184.17   $184.15   $184.20  
  Purchase #2 $146.93   10.241%   $161.9771   $161.98   $162.00   $162.00  
  Purchase #3 $139.50   8.823%   $151.8081   $151.81   $151.80   $151.80  
  Purchase #4 $122.93   11.291%   $136.81   $136.81   $136.80   $136.80  
  Purchase #5 $158.67   11.511%   $176.9345   $176.93   $176.95   $176.90  
  Purchase #6 $23.47   13.628%   $26.6685   $26.67   $26.65   $26.70  
  Purchase #7 $182.92   12.293%   $205.4064   $205.41   $205.40   $205.40  
  7 purchase totals = $940.94       $1,043.7741   $1,043.78   $1,043.75   $1,043.80