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	$109.36	13.322%	$123.9289	$123.93	$123.95	$123.90
Purchase #2	$150.32	9.726%	$164.9401	$164.94	$164.95	$164.90
Purchase #3	$87.57	6.759%	$93.4889	$93.49	$93.50	$93.50
Purchase #4	$180.39	8.794%	$196.2535	$196.25	$196.25	$196.30
Purchase #5	$191.74	7.581%	$206.2758	$206.28	$206.30	$206.30
Purchase #6	$42.55	4.605%	$44.5094	$44.51	$44.50	$44.50
Purchase #7	$65.90	7.421%	$70.7904	$70.79	$70.80	$70.80
7 purchase totals =	$827.83		$900.1870	$900.19	$900.25	$900.20