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 $165.65   9.383%   $181.1929   $181.19   $181.20   $181.20  
  Purchase #2 $23.30   3.490%   $24.1132   $24.11   $24.10   $24.10  
  Purchase #3 $239.40   4.526%   $250.2352   $250.24   $250.25   $250.20  
  Purchase #4 $54.34   6.842%   $58.0579   $58.06   $58.05   $58.10  
  Purchase #5 $154.77   6.383%   $164.649   $164.65   $164.65   $164.60  
  Purchase #6 $146.74   9.853%   $161.1983   $161.20   $161.20   $161.20  
  Purchase #7 $106.88   3.669%   $110.8014   $110.80   $110.80   $110.80  
  7 purchase totals = $891.08       $950.2479   $950.25   $950.25   $950.20