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 $63.58   12.538%   $71.5517   $71.55   $71.55   $71.60  
  Purchase #2 $212.35   13.243%   $240.4715   $240.47   $240.45   $240.50  
  Purchase #3 $61.41   5.242%   $64.6291   $64.63   $64.65   $64.60  
  Purchase #4 $73.76   10.747%   $81.687   $81.69   $81.70   $81.70  
  Purchase #5 $134.50   8.398%   $145.7953   $145.80   $145.80   $145.80  
  Purchase #6 $223.67   8.495%   $242.6708   $242.67   $242.65   $242.70  
  Purchase #7 $66.71   6.671%   $71.1602   $71.16   $71.15   $71.20  
  7 purchase totals = $835.98       $917.9656   $917.97   $917.95   $918.10