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 $177.69   9.191%   $194.0215   $194.02   $194.00   $194.00  
  Purchase #2 $169.28   13.828%   $192.688   $192.69   $192.70   $192.70  
  Purchase #3 $137.87   8.822%   $150.0329   $150.03   $150.05   $150.00  
  Purchase #4 $23.66   11.789%   $26.4493   $26.45   $26.45   $26.40  
  Purchase #5 $86.79   10.721%   $96.0948   $96.09   $96.10   $96.10  
  Purchase #6 $63.84   6.852%   $68.2143   $68.21   $68.20   $68.20  
  Purchase #7 $237.77   13.229%   $269.2246   $269.22   $269.20   $269.20  
  7 purchase totals = $896.90       $996.7254   $996.71   $996.70   $996.60