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 $208.74   11.298%   $232.3234   $232.32   $232.30   $232.30  
  Purchase #2 $86.46   12.565%   $97.3237   $97.32   $97.30   $97.30  
  Purchase #3 $178.99   4.480%   $187.0088   $187.01   $187.00   $187.00  
  Purchase #4 $234.35   7.828%   $252.6949   $252.69   $252.70   $252.70  
  Purchase #5 $43.95   10.252%   $48.4558   $48.46   $48.45   $48.50  
  Purchase #6 $188.60   9.559%   $206.6283   $206.63   $206.65   $206.60  
  Purchase #7 $39.82   9.108%   $43.4468   $43.45   $43.45   $43.40  
  7 purchase totals = $980.91       $1,067.8817   $1,067.88   $1,067.85   $1,067.80