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 $241.79   8.221%   $261.6676   $261.67   $261.65   $261.70  
  Purchase #2 $80.53   11.440%   $89.7426   $89.74   $89.75   $89.70  
  Purchase #3 $182.80   11.725%   $204.2333   $204.23   $204.25   $204.20  
  Purchase #4 $163.98   6.196%   $174.1402   $174.14   $174.15   $174.10  
  Purchase #5 $95.27   5.318%   $100.3365   $100.34   $100.35   $100.30  
  Purchase #6 $211.98   3.475%   $219.3463   $219.35   $219.35   $219.30  
  Purchase #7 $60.69   10.386%   $66.9933   $66.99   $67.00   $67.00  
  7 purchase totals = $1,037.04       $1,116.4598   $1,116.46   $1,116.50   $1,116.30