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 $208.98   12.384%   $234.8601   $234.86   $234.85   $234.90  
  Purchase #2 $186.75   12.693%   $210.4542   $210.45   $210.45   $210.50  
  Purchase #3 $193.89   12.653%   $218.4229   $218.42   $218.40   $218.40  
  Purchase #4 $44.94   3.786%   $46.6414   $46.64   $46.65   $46.60  
  Purchase #5 $198.39   6.270%   $210.8291   $210.83   $210.85   $210.80  
  Purchase #6 $214.87   5.361%   $226.3892   $226.39   $226.40   $226.40  
  Purchase #7 $57.91   12.128%   $64.9333   $64.93   $64.95   $64.90  
  7 purchase totals = $1,105.73       $1,212.5302   $1,212.52   $1,212.55   $1,212.50