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 $34.75   11.514%   $38.7511   $38.75   $38.75   $38.80  
  Purchase #2 $101.51   8.824%   $110.4672   $110.47   $110.45   $110.50  
  Purchase #3 $231.66   7.439%   $248.8932   $248.89   $248.90   $248.90  
  Purchase #4 $113.72   6.513%   $121.1266   $121.13   $121.15   $121.10  
  Purchase #5 $96.75   13.380%   $109.6952   $109.70   $109.70   $109.70  
  Purchase #6 $212.26   5.586%   $224.1168   $224.12   $224.10   $224.10  
  Purchase #7 $156.27   4.433%   $163.1974   $163.20   $163.20   $163.20  
  7 purchase totals = $946.92       $1,016.2475   $1,016.26   $1,016.25   $1,016.30