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 $227.27   11.447%   $253.2856   $253.29   $253.30   $253.30  
  Purchase #2 $109.41   4.218%   $114.0249   $114.02   $114.00   $114.00  
  Purchase #3 $136.52   11.642%   $152.4137   $152.41   $152.40   $152.40  
  Purchase #4 $36.35   6.574%   $38.7396   $38.74   $38.75   $38.70  
  Purchase #5 $246.26   4.394%   $257.0807   $257.08   $257.10   $257.10  
  Purchase #6 $18.36   11.770%   $20.521   $20.52   $20.50   $20.50  
  Purchase #7 $188.97   12.861%   $213.2734   $213.27   $213.25   $213.30  
  7 purchase totals = $963.14       $1,049.3389   $1,049.33   $1,049.30   $1,049.30