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 $179.25   11.578%   $200.0036   $200.00   $200.00   $200.00  
  Purchase #2 $101.44   4.868%   $106.3781   $106.38   $106.40   $106.40  
  Purchase #3 $51.36   6.413%   $54.6537   $54.65   $54.65   $54.70  
  Purchase #4 $107.28   9.501%   $117.4727   $117.47   $117.45   $117.50  
  Purchase #5 $181.74   6.271%   $193.1369   $193.14   $193.15   $193.10  
  Purchase #6 $199.98   4.115%   $208.2092   $208.21   $208.20   $208.20  
  Purchase #7 $165.46   13.336%   $187.5257   $187.53   $187.55   $187.50  
  7 purchase totals = $986.51       $1,067.3799   $1,067.38   $1,067.40   $1,067.40