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 $203.62   5.807%   $215.4442   $215.44   $215.45   $215.40  
  Purchase #2 $161.63   8.327%   $175.0889   $175.09   $175.10   $175.10  
  Purchase #3 $167.68   3.616%   $173.7433   $173.74   $173.75   $173.70  
  Purchase #4 $177.81   13.331%   $201.5139   $201.51   $201.50   $201.50  
  Purchase #5 $24.34   6.307%   $25.8751   $25.88   $25.90   $25.90  
  Purchase #6 $159.45   3.587%   $165.1695   $165.17   $165.15   $165.20  
  Purchase #7 $37.45   11.187%   $41.6395   $41.64   $41.65   $41.60  
  7 purchase totals = $931.98       $998.4744   $998.47   $998.50   $998.40