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 $68.37   7.326%   $73.3788   $73.38   $73.40   $73.40  
  Purchase #2 $37.70   8.689%   $40.9758   $40.98   $41.00   $41.00  
  Purchase #3 $73.55   4.733%   $77.0311   $77.03   $77.05   $77.00  
  Purchase #4 $151.94   6.484%   $161.7918   $161.79   $161.80   $161.80  
  Purchase #5 $208.97   3.695%   $216.6914   $216.69   $216.70   $216.70  
  Purchase #6 $180.52   6.729%   $192.6672   $192.67   $192.65   $192.70  
  Purchase #7 $28.44   9.420%   $31.119   $31.12   $31.10   $31.10  
  7 purchase totals = $749.49       $793.6551   $793.66   $793.70   $793.70