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 $202.25   5.462%   $213.2969   $213.30   $213.30   $213.30  
  Purchase #2 $44.32   11.366%   $49.3574   $49.36   $49.35   $49.40  
  Purchase #3 $178.61   12.677%   $201.2524   $201.25   $201.25   $201.30  
  Purchase #4 $74.58   12.467%   $83.8779   $83.88   $83.90   $83.90  
  Purchase #5 $187.73   7.533%   $201.8717   $201.87   $201.85   $201.90  
  Purchase #6 $107.92   7.619%   $116.1424   $116.14   $116.15   $116.10  
  Purchase #7 $165.74   3.158%   $170.9741   $170.97   $170.95   $171.00  
  7 purchase totals = $961.15       $1,036.7728   $1,036.77   $1,036.75   $1,036.90