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 $119.58   5.772%   $126.4822   $126.48   $126.50   $126.50  
  Purchase #2 $246.34   11.216%   $273.9695   $273.97   $273.95   $274.00  
  Purchase #3 $66.59   4.221%   $69.4008   $69.40   $69.40   $69.40  
  Purchase #4 $76.82   13.856%   $87.4642   $87.46   $87.45   $87.50  
  Purchase #5 $109.59   4.164%   $114.1533   $114.15   $114.15   $114.20  
  Purchase #6 $173.44   4.576%   $181.3766   $181.38   $181.40   $181.40  
  Purchase #7 $138.79   12.349%   $155.9292   $155.93   $155.95   $155.90  
  7 purchase totals = $931.15       $1,008.7758   $1,008.77   $1,008.80   $1,008.90