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 $177.40   8.800%   $193.0112   $193.01   $193.00   $193.00  
  Purchase #2 $216.85   10.199%   $238.9665   $238.97   $238.95   $239.00  
  Purchase #3 $20.33   11.168%   $22.6005   $22.60   $22.60   $22.60  
  Purchase #4 $125.48   9.369%   $137.2362   $137.24   $137.25   $137.20  
  Purchase #5 $52.80   6.539%   $56.2526   $56.25   $56.25   $56.30  
  Purchase #6 $179.43   3.581%   $185.8554   $185.86   $185.85   $185.90  
  Purchase #7 $93.29   10.470%   $103.0575   $103.06   $103.05   $103.10  
  7 purchase totals = $865.58       $936.9799   $936.99   $936.95   $937.10