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 $127.92   13.821%   $145.5998   $145.60   $145.60   $145.60  
  Purchase #2 $51.74   9.294%   $56.5487   $56.55   $56.55   $56.50  
  Purchase #3 $11.54   6.316%   $12.2689   $12.27   $12.25   $12.30  
  Purchase #4 $202.92   8.394%   $219.9531   $219.95   $219.95   $220.00  
  Purchase #5 $51.90   3.661%   $53.8001   $53.80   $53.80   $53.80  
  Purchase #6 $245.68   3.796%   $255.006   $255.01   $255.00   $255.00  
  Purchase #7 $98.42   7.597%   $105.897   $105.90   $105.90   $105.90  
  7 purchase totals = $790.12       $849.0736   $849.08   $849.05   $849.10