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 $187.33   6.255%   $199.0475   $199.05   $199.05   $199.00  
  Purchase #2 $237.40   8.276%   $257.0472   $257.05   $257.05   $257.00  
  Purchase #3 $50.59   12.134%   $56.7286   $56.73   $56.75   $56.70  
  Purchase #4 $76.57   11.440%   $85.3296   $85.33   $85.35   $85.30  
  Purchase #5 $193.49   5.156%   $203.4663   $203.47   $203.45   $203.50  
  Purchase #6 $116.56   5.703%   $123.2074   $123.21   $123.20   $123.20  
  Purchase #7 $73.76   10.643%   $81.6103   $81.61   $81.60   $81.60  
  7 purchase totals = $935.70       $1,006.4369   $1,006.45   $1,006.45   $1,006.30