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 $61.37   9.699%   $67.3223   $67.32   $67.30   $67.30  
  Purchase #2 $211.56   5.458%   $223.1069   $223.11   $223.10   $223.10  
  Purchase #3 $161.51   11.817%   $180.5956   $180.60   $180.60   $180.60  
  Purchase #4 $101.38   4.364%   $105.8042   $105.80   $105.80   $105.80  
  Purchase #5 $84.89   8.821%   $92.3781   $92.38   $92.40   $92.40  
  Purchase #6 $153.39   12.186%   $172.0821   $172.08   $172.10   $172.10  
  Purchase #7 $85.98   13.638%   $97.706   $97.71   $97.70   $97.70  
  7 purchase totals = $860.08       $938.9952   $939.00   $939.00   $939.00