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 $246.52   9.318%   $269.4907   $269.49   $269.50   $269.50  
  Purchase #2 $112.93   10.485%   $124.7707   $124.77   $124.75   $124.80  
  Purchase #3 $30.93   13.635%   $35.1473   $35.15   $35.15   $35.10  
  Purchase #4 $219.33   8.166%   $237.2405   $237.24   $237.25   $237.20  
  Purchase #5 $115.89   8.388%   $125.6109   $125.61   $125.60   $125.60  
  Purchase #6 $40.36   9.554%   $44.216   $44.22   $44.20   $44.20  
  Purchase #7 $213.66   5.496%   $225.4028   $225.40   $225.40   $225.40  
  7 purchase totals = $979.62       $1,061.8789   $1,061.88   $1,061.85   $1,061.80