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 $89.58   5.475%   $94.4845   $94.48   $94.50   $94.50  
  Purchase #2 $124.96   9.294%   $136.5738   $136.57   $136.55   $136.60  
  Purchase #3 $249.54   8.167%   $269.9199   $269.92   $269.90   $269.90  
  Purchase #4 $92.62   12.767%   $104.4448   $104.44   $104.45   $104.40  
  Purchase #5 $207.87   11.507%   $231.7896   $231.79   $231.80   $231.80  
  Purchase #6 $199.34   11.215%   $221.696   $221.70   $221.70   $221.70  
  Purchase #7 $16.27   4.616%   $17.021   $17.02   $17.00   $17.00  
  7 purchase totals = $980.18       $1,075.9296   $1,075.92   $1,075.90   $1,075.90