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 $155.37   13.107%   $175.7343   $175.73   $175.75   $175.70  
  Purchase #2 $52.37   6.873%   $55.9694   $55.97   $55.95   $56.00  
  Purchase #3 $160.54   3.209%   $165.6917   $165.69   $165.70   $165.70  
  Purchase #4 $107.54   8.738%   $116.9368   $116.94   $116.95   $116.90  
  Purchase #5 $250.70   6.789%   $267.72   $267.72   $267.70   $267.70  
  Purchase #6 $188.42   12.828%   $212.5905   $212.59   $212.60   $212.60  
  Purchase #7 $208.68   4.746%   $218.584   $218.58   $218.60   $218.60  
  7 purchase totals = $1,123.62       $1,213.2267   $1,213.22   $1,213.25   $1,213.20