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 $82.52   4.497%   $86.2309   $86.23   $86.25   $86.20  
  Purchase #2 $148.39   11.202%   $165.0126   $165.01   $165.00   $165.00  
  Purchase #3 $46.99   9.601%   $51.5015   $51.50   $51.50   $51.50  
  Purchase #4 $54.29   11.628%   $60.6028   $60.60   $60.60   $60.60  
  Purchase #5 $224.78   8.591%   $244.0908   $244.09   $244.10   $244.10  
  Purchase #6 $86.42   6.422%   $91.9699   $91.97   $91.95   $92.00  
  Purchase #7 $171.82   10.395%   $189.6807   $189.68   $189.70   $189.70  
  7 purchase totals = $815.21       $889.0892   $889.08   $889.10   $889.10