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 $81.91   13.573%   $93.0276   $93.03   $93.05   $93.00  
  Purchase #2 $85.87   11.604%   $95.8344   $95.83   $95.85   $95.80  
  Purchase #3 $186.87   13.689%   $212.4506   $212.45   $212.45   $212.50  
  Purchase #4 $73.37   10.105%   $80.784   $80.78   $80.80   $80.80  
  Purchase #5 $186.66   11.555%   $208.2286   $208.23   $208.25   $208.20  
  Purchase #6 $148.61   13.160%   $168.1671   $168.17   $168.15   $168.20  
  Purchase #7 $160.40   10.139%   $176.663   $176.66   $176.65   $176.70  
  7 purchase totals = $923.69       $1,035.1553   $1,035.15   $1,035.20   $1,035.20