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 $64.62   6.715%   $68.9592   $68.96   $68.95   $69.00  
  Purchase #2 $189.85   10.766%   $210.2893   $210.29   $210.30   $210.30  
  Purchase #3 $184.48   11.705%   $206.0734   $206.07   $206.05   $206.10  
  Purchase #4 $191.65   13.722%   $217.9482   $217.95   $217.95   $217.90  
  Purchase #5 $98.72   10.282%   $108.8704   $108.87   $108.85   $108.90  
  Purchase #6 $173.63   4.309%   $181.1117   $181.11   $181.10   $181.10  
  Purchase #7 $222.63   11.534%   $248.3081   $248.31   $248.30   $248.30  
  7 purchase totals = $1,125.58       $1,241.5603   $1,241.56   $1,241.50   $1,241.60