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 $91.82   4.821%   $96.2466   $96.25   $96.25   $96.20  
  Purchase #2 $137.82   6.280%   $146.4751   $146.48   $146.50   $146.50  
  Purchase #3 $10.56   6.607%   $11.2577   $11.26   $11.25   $11.30  
  Purchase #4 $169.87   4.513%   $177.5362   $177.54   $177.55   $177.50  
  Purchase #5 $132.65   3.338%   $137.0779   $137.08   $137.10   $137.10  
  Purchase #6 $239.63   8.859%   $260.8588   $260.86   $260.85   $260.90  
  Purchase #7 $241.57   7.476%   $259.6298   $259.63   $259.65   $259.60  
  7 purchase totals = $1,023.92       $1,089.0821   $1,089.10   $1,089.15   $1,089.10