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 $69.31   10.434%   $76.5418   $76.54   $76.55   $76.50  
  Purchase #2 $10.76   5.608%   $11.3634   $11.36   $11.35   $11.40  
  Purchase #3 $153.46   7.672%   $165.2335   $165.23   $165.25   $165.20  
  Purchase #4 $165.72   8.467%   $179.7515   $179.75   $179.75   $179.80  
  Purchase #5 $167.56   5.849%   $177.3606   $177.36   $177.35   $177.40  
  Purchase #6 $239.97   8.228%   $259.7147   $259.71   $259.70   $259.70  
  Purchase #7 $47.86   12.585%   $53.8832   $53.88   $53.90   $53.90  
  7 purchase totals = $854.64       $923.8487   $923.83   $923.85   $923.90