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 $166.66   11.455%   $185.7509   $185.75   $185.75   $185.80  
  Purchase #2 $218.89   12.636%   $246.5489   $246.55   $246.55   $246.50  
  Purchase #3 $18.90   3.317%   $19.5269   $19.53   $19.55   $19.50  
  Purchase #4 $127.29   6.597%   $135.6873   $135.69   $135.70   $135.70  
  Purchase #5 $190.69   8.565%   $207.0226   $207.02   $207.00   $207.00  
  Purchase #6 $245.39   9.811%   $269.4652   $269.47   $269.45   $269.50  
  Purchase #7 $138.87   10.177%   $153.0028   $153.00   $153.00   $153.00  
  7 purchase totals = $1,106.69       $1,217.0046   $1,217.01   $1,217.00   $1,217.00