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 $63.51   12.774%   $71.6228   $71.62   $71.60   $71.60  
  Purchase #2 $94.91   3.232%   $97.9775   $97.98   $98.00   $98.00  
  Purchase #3 $26.40   9.129%   $28.8101   $28.81   $28.80   $28.80  
  Purchase #4 $104.51   13.280%   $118.3889   $118.39   $118.40   $118.40  
  Purchase #5 $68.29   13.556%   $77.5474   $77.55   $77.55   $77.50  
  Purchase #6 $155.72   8.771%   $169.3782   $169.38   $169.40   $169.40  
  Purchase #7 $53.36   11.820%   $59.6672   $59.67   $59.65   $59.70  
  7 purchase totals = $566.70       $623.3921   $623.40   $623.40   $623.40