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 $52.26   9.789%   $57.3757   $57.38   $57.40   $57.40  
  Purchase #2 $244.97   13.129%   $277.1321   $277.13   $277.15   $277.10  
  Purchase #3 $228.30   7.546%   $245.5275   $245.53   $245.55   $245.50  
  Purchase #4 $129.76   10.701%   $143.6456   $143.65   $143.65   $143.60  
  Purchase #5 $238.33   12.256%   $267.5397   $267.54   $267.55   $267.50  
  Purchase #6 $157.36   13.822%   $179.1103   $179.11   $179.10   $179.10  
  Purchase #7 $34.29   10.568%   $37.9138   $37.91   $37.90   $37.90  
  7 purchase totals = $1,085.27       $1,208.2447   $1,208.25   $1,208.30   $1,208.10