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 $54.64   13.416%   $61.9705   $61.97   $61.95   $62.00  
  Purchase #2 $21.60   7.210%   $23.1574   $23.16   $23.15   $23.20  
  Purchase #3 $241.26   12.183%   $270.6527   $270.65   $270.65   $270.70  
  Purchase #4 $32.38   5.188%   $34.0599   $34.06   $34.05   $34.10  
  Purchase #5 $171.82   5.616%   $181.4694   $181.47   $181.45   $181.50  
  Purchase #6 $57.76   11.279%   $64.2748   $64.27   $64.25   $64.30  
  Purchase #7 $35.48   13.604%   $40.3067   $40.31   $40.30   $40.30  
  7 purchase totals = $614.94       $675.8914   $675.89   $675.80   $676.10