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 $150.29   7.778%   $161.9796   $161.98   $162.00   $162.00  
  Purchase #2 $9.50   13.725%   $10.8039   $10.80   $10.80   $10.80  
  Purchase #3 $89.76   5.796%   $94.9625   $94.96   $94.95   $95.00  
  Purchase #4 $114.29   10.613%   $126.4196   $126.42   $126.40   $126.40  
  Purchase #5 $204.60   13.217%   $231.642   $231.64   $231.65   $231.60  
  Purchase #6 $168.54   5.678%   $178.1097   $178.11   $178.10   $178.10  
  Purchase #7 $87.63   12.151%   $98.2779   $98.28   $98.30   $98.30  
  7 purchase totals = $824.61       $902.1952   $902.19   $902.20   $902.20