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 $75.68   12.370%   $85.0416   $85.04   $85.05   $85.00  
  Purchase #2 $185.87   6.373%   $197.7155   $197.72   $197.70   $197.70  
  Purchase #3 $197.74   6.549%   $210.69   $210.69   $210.70   $210.70  
  Purchase #4 $208.44   6.786%   $222.5847   $222.58   $222.60   $222.60  
  Purchase #5 $32.27   8.147%   $34.899   $34.90   $34.90   $34.90  
  Purchase #6 $160.55   8.450%   $174.1165   $174.12   $174.10   $174.10  
  Purchase #7 $75.93   13.741%   $86.3635   $86.36   $86.35   $86.40  
  7 purchase totals = $936.48       $1,011.4108   $1,011.41   $1,011.40   $1,011.40