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 $223.52   12.616%   $251.7193   $251.72   $251.70   $251.70  
  Purchase #2 $116.96   6.832%   $124.9507   $124.95   $124.95   $125.00  
  Purchase #3 $183.68   12.143%   $205.9843   $205.98   $206.00   $206.00  
  Purchase #4 $241.47   4.345%   $251.9619   $251.96   $251.95   $252.00  
  Purchase #5 $208.95   4.504%   $218.3611   $218.36   $218.35   $218.40  
  Purchase #6 $86.46   5.438%   $91.1617   $91.16   $91.15   $91.20  
  Purchase #7 $107.36   7.469%   $115.3787   $115.38   $115.40   $115.40  
  7 purchase totals = $1,168.40       $1,259.5177   $1,259.51   $1,259.50   $1,259.70