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 $92.52   12.501%   $104.0859   $104.09   $104.10   $104.10  
  Purchase #2 $5.97   9.301%   $6.5253   $6.53   $6.55   $6.50  
  Purchase #3 $229.72   13.255%   $260.1694   $260.17   $260.15   $260.20  
  Purchase #4 $105.90   9.346%   $115.7974   $115.80   $115.80   $115.80  
  Purchase #5 $48.42   12.563%   $54.503   $54.50   $54.50   $54.50  
  Purchase #6 $206.36   12.805%   $232.7844   $232.78   $232.80   $232.80  
  Purchase #7 $114.86   10.269%   $126.655   $126.66   $126.65   $126.70  
  7 purchase totals = $803.75       $900.5204   $900.53   $900.55   $900.60