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 $34.67   9.713%   $38.0375   $38.04   $38.05   $38.00  
  Purchase #2 $40.91   13.557%   $46.4562   $46.46   $46.45   $46.50  
  Purchase #3 $149.36   12.333%   $167.7806   $167.78   $167.80   $167.80  
  Purchase #4 $178.59   8.574%   $193.9023   $193.90   $193.90   $193.90  
  Purchase #5 $208.98   3.795%   $216.9108   $216.91   $216.90   $216.90  
  Purchase #6 $214.66   6.438%   $228.4798   $228.48   $228.50   $228.50  
  Purchase #7 $48.31   7.255%   $51.8149   $51.81   $51.80   $51.80  
  7 purchase totals = $875.48       $943.3821   $943.38   $943.40   $943.40