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 $6.95   8.640%   $7.5505   $7.55   $7.55   $7.60  
  Purchase #2 $223.71   13.368%   $253.6156   $253.62   $253.60   $253.60  
  Purchase #3 $111.65   7.206%   $119.6955   $119.70   $119.70   $119.70  
  Purchase #4 $86.89   13.562%   $98.674   $98.67   $98.65   $98.70  
  Purchase #5 $164.96   6.437%   $175.5785   $175.58   $175.60   $175.60  
  Purchase #6 $74.33   5.641%   $78.523   $78.52   $78.50   $78.50  
  Purchase #7 $227.35   11.108%   $252.604   $252.60   $252.60   $252.60  
  7 purchase totals = $895.84       $986.2411   $986.24   $986.20   $986.30