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 $192.28   11.134%   $213.6885   $213.69   $213.70   $213.70  
  Purchase #2 $205.51   3.106%   $211.8931   $211.89   $211.90   $211.90  
  Purchase #3 $70.52   10.640%   $78.0233   $78.02   $78.00   $78.00  
  Purchase #4 $93.97   3.488%   $97.2477   $97.25   $97.25   $97.20  
  Purchase #5 $214.88   5.202%   $226.0581   $226.06   $226.05   $226.10  
  Purchase #6 $70.91   9.607%   $77.7223   $77.72   $77.70   $77.70  
  Purchase #7 $31.68   6.133%   $33.6229   $33.62   $33.60   $33.60  
  7 purchase totals = $879.75       $938.2559   $938.25   $938.20   $938.20