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 $246.43   11.725%   $275.3239   $275.32   $275.30   $275.30  
  Purchase #2 $9.86   10.712%   $10.9162   $10.92   $10.90   $10.90  
  Purchase #3 $211.55   12.265%   $237.4966   $237.50   $237.50   $237.50  
  Purchase #4 $160.70   3.663%   $166.5864   $166.59   $166.60   $166.60  
  Purchase #5 $25.49   10.361%   $28.131   $28.13   $28.15   $28.10  
  Purchase #6 $241.27   8.871%   $262.6731   $262.67   $262.65   $262.70  
  Purchase #7 $42.50   9.338%   $46.4687   $46.47   $46.45   $46.50  
  7 purchase totals = $937.80       $1,027.5959   $1,027.60   $1,027.55   $1,027.60