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 $211.34   11.153%   $234.9108   $234.91   $234.90   $234.90  
  Purchase #2 $212.68   9.388%   $232.6464   $232.65   $232.65   $232.60  
  Purchase #3 $76.57   12.326%   $86.008   $86.01   $86.00   $86.00  
  Purchase #4 $164.85   4.483%   $172.2402   $172.24   $172.25   $172.20  
  Purchase #5 $43.58   6.206%   $46.2846   $46.28   $46.30   $46.30  
  Purchase #6 $122.95   11.660%   $137.286   $137.29   $137.30   $137.30  
  Purchase #7 $65.79   6.484%   $70.0558   $70.06   $70.05   $70.10  
  7 purchase totals = $897.76       $979.4318   $979.44   $979.45   $979.40