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 $63.41   13.440%   $71.9323   $71.93   $71.95   $71.90  
  Purchase #2 $192.72   11.531%   $214.9425   $214.94   $214.95   $214.90  
  Purchase #3 $137.66   4.159%   $143.3853   $143.39   $143.40   $143.40  
  Purchase #4 $6.61   11.465%   $7.3678   $7.37   $7.35   $7.40  
  Purchase #5 $143.38   4.320%   $149.574   $149.57   $149.55   $149.60  
  Purchase #6 $177.73   13.552%   $201.816   $201.82   $201.80   $201.80  
  Purchase #7 $148.71   13.479%   $168.7546   $168.75   $168.75   $168.80  
  7 purchase totals = $870.22       $957.7725   $957.77   $957.75   $957.80