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 $87.94   9.215%   $96.0437   $96.04   $96.05   $96.00  
  Purchase #2 $52.51   7.247%   $56.3154   $56.32   $56.30   $56.30  
  Purchase #3 $176.30   9.615%   $193.2512   $193.25   $193.25   $193.30  
  Purchase #4 $174.57   13.140%   $197.5085   $197.51   $197.50   $197.50  
  Purchase #5 $217.94   13.248%   $246.8127   $246.81   $246.80   $246.80  
  Purchase #6 $10.80   5.287%   $11.371   $11.37   $11.35   $11.40  
  Purchase #7 $207.91   4.672%   $217.6236   $217.62   $217.60   $217.60  
  7 purchase totals = $927.97       $1,018.9261   $1,018.92   $1,018.85   $1,018.90