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 $60.79   11.135%   $67.559   $67.56   $67.55   $67.60  
  Purchase #2 $164.59   10.611%   $182.0546   $182.05   $182.05   $182.10  
  Purchase #3 $174.87   4.833%   $183.3215   $183.32   $183.30   $183.30  
  Purchase #4 $34.72   6.323%   $36.9153   $36.92   $36.90   $36.90  
  Purchase #5 $161.87   7.296%   $173.68   $173.68   $173.70   $173.70  
  Purchase #6 $111.80   9.182%   $122.0655   $122.07   $122.05   $122.10  
  Purchase #7 $80.82   13.774%   $91.9521   $91.95   $91.95   $92.00  
  7 purchase totals = $789.46       $857.5480   $857.55   $857.50   $857.70