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 $52.93   11.153%   $58.8333   $58.83   $58.85   $58.80  
  Purchase #2 $101.27   13.222%   $114.6599   $114.66   $114.65   $114.70  
  Purchase #3 $220.89   11.494%   $246.2791   $246.28   $246.30   $246.30  
  Purchase #4 $189.31   4.209%   $197.2781   $197.28   $197.30   $197.30  
  Purchase #5 $160.59   11.201%   $178.5777   $178.58   $178.60   $178.60  
  Purchase #6 $35.54   9.544%   $38.9319   $38.93   $38.95   $38.90  
  Purchase #7 $173.47   5.264%   $182.6015   $182.60   $182.60   $182.60  
  7 purchase totals = $934.00       $1,017.1615   $1,017.16   $1,017.25   $1,017.20