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 $162.56   13.702%   $184.834   $184.83   $184.85   $184.80  
  Purchase #2 $82.91   12.172%   $93.0018   $93.00   $93.00   $93.00  
  Purchase #3 $73.72   3.281%   $76.1388   $76.14   $76.15   $76.10  
  Purchase #4 $66.59   10.311%   $73.4561   $73.46   $73.45   $73.50  
  Purchase #5 $48.75   3.795%   $50.6001   $50.60   $50.60   $50.60  
  Purchase #6 $90.65   5.556%   $95.6865   $95.69   $95.70   $95.70  
  Purchase #7 $201.65   9.775%   $221.3613   $221.36   $221.35   $221.40  
  7 purchase totals = $726.83       $795.0786   $795.08   $795.10   $795.10