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 $246.45   8.731%   $267.9675   $267.97   $267.95   $268.00  
  Purchase #2 $74.44   5.449%   $78.4962   $78.50   $78.50   $78.50  
  Purchase #3 $100.95   13.616%   $114.6954   $114.70   $114.70   $114.70  
  Purchase #4 $116.88   5.610%   $123.437   $123.44   $123.45   $123.40  
  Purchase #5 $241.82   12.455%   $271.9387   $271.94   $271.95   $271.90  
  Purchase #6 $203.89   5.871%   $215.8604   $215.86   $215.85   $215.90  
  Purchase #7 $145.53   5.440%   $153.4468   $153.45   $153.45   $153.40  
  7 purchase totals = $1,129.96       $1,225.8420   $1,225.86   $1,225.85   $1,225.80