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 $97.45   8.789%   $106.0149   $106.01   $106.00   $106.00  
  Purchase #2 $240.92   6.105%   $255.6282   $255.63   $255.65   $255.60  
  Purchase #3 $148.78   13.117%   $168.2955   $168.30   $168.30   $168.30  
  Purchase #4 $193.28   9.564%   $211.7653   $211.77   $211.75   $211.80  
  Purchase #5 $141.88   3.397%   $146.6997   $146.70   $146.70   $146.70  
  Purchase #6 $118.66   8.810%   $129.1139   $129.11   $129.10   $129.10  
  Purchase #7 $75.97   9.530%   $83.2099   $83.21   $83.20   $83.20  
  7 purchase totals = $1,016.94       $1,100.7274   $1,100.73   $1,100.70   $1,100.70