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 $143.53   12.866%   $161.9966   $162.00   $162.00   $162.00  
  Purchase #2 $72.43   4.174%   $75.4532   $75.45   $75.45   $75.50  
  Purchase #3 $57.90   6.109%   $61.4371   $61.44   $61.45   $61.40  
  Purchase #4 $247.69   6.301%   $263.2969   $263.30   $263.30   $263.30  
  Purchase #5 $5.47   13.271%   $6.1959   $6.20   $6.20   $6.20  
  Purchase #6 $54.38   7.855%   $58.6515   $58.65   $58.65   $58.70  
  Purchase #7 $173.60   13.296%   $196.6819   $196.68   $196.70   $196.70  
  7 purchase totals = $755.00       $823.7131   $823.72   $823.75   $823.80