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 $163.96   3.537%   $169.7593   $169.76   $169.75   $169.80  
  Purchase #2 $211.61   4.141%   $220.3728   $220.37   $220.35   $220.40  
  Purchase #3 $200.28   10.612%   $221.5337   $221.53   $221.55   $221.50  
  Purchase #4 $73.96   13.200%   $83.7227   $83.72   $83.70   $83.70  
  Purchase #5 $191.62   13.716%   $217.9026   $217.90   $217.90   $217.90  
  Purchase #6 $68.25   13.752%   $77.6357   $77.64   $77.65   $77.60  
  Purchase #7 $62.49   4.613%   $65.3727   $65.37   $65.35   $65.40  
  7 purchase totals = $972.17       $1,056.2995   $1,056.29   $1,056.25   $1,056.30