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 $63.86   11.206%   $71.0162   $71.02   $71.00   $71.00  
  Purchase #2 $167.54   3.842%   $173.9769   $173.98   $174.00   $174.00  
  Purchase #3 $230.46   13.581%   $261.7588   $261.76   $261.75   $261.80  
  Purchase #4 $151.47   3.430%   $156.6654   $156.67   $156.65   $156.70  
  Purchase #5 $204.69   12.388%   $230.047   $230.05   $230.05   $230.00  
  Purchase #6 $191.98   6.702%   $204.8465   $204.85   $204.85   $204.80  
  Purchase #7 $189.32   4.389%   $197.6293   $197.63   $197.65   $197.60  
  7 purchase totals = $1,199.32       $1,295.9401   $1,295.96   $1,295.95   $1,295.90