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 $216.61   6.506%   $230.7026   $230.70   $230.70   $230.70  
  Purchase #2 $156.51   4.674%   $163.8253   $163.83   $163.85   $163.80  
  Purchase #3 $151.77   7.633%   $163.3546   $163.35   $163.35   $163.40  
  Purchase #4 $234.59   5.648%   $247.8396   $247.84   $247.85   $247.80  
  Purchase #5 $245.70   4.821%   $257.5452   $257.55   $257.55   $257.50  
  Purchase #6 $29.93   13.348%   $33.9251   $33.93   $33.95   $33.90  
  Purchase #7 $230.34   7.186%   $246.8922   $246.89   $246.90   $246.90  
  7 purchase totals = $1,265.45       $1,344.0846   $1,344.09   $1,344.15   $1,344.00