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 $147.50   11.868%   $165.0053   $165.01   $165.00   $165.00  
  Purchase #2 $84.97   10.231%   $93.6633   $93.66   $93.65   $93.70  
  Purchase #3 $16.78   10.699%   $18.5753   $18.58   $18.60   $18.60  
  Purchase #4 $75.64   7.430%   $81.2601   $81.26   $81.25   $81.30  
  Purchase #5 $122.53   3.455%   $126.7634   $126.76   $126.75   $126.80  
  Purchase #6 $208.25   4.391%   $217.3943   $217.39   $217.40   $217.40  
  Purchase #7 $192.84   4.765%   $202.0288   $202.03   $202.05   $202.00  
  7 purchase totals = $848.51       $904.6905   $904.69   $904.70   $904.80