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	$37.78	5.745%	$39.9505	$39.95	$39.95	$40.00
Purchase #2	$213.88	11.461%	$238.3928	$238.39	$238.40	$238.40
Purchase #3	$27.82	3.451%	$28.7801	$28.78	$28.80	$28.80
Purchase #4	$250.55	7.834%	$270.1781	$270.18	$270.20	$270.20
Purchase #5	$111.74	5.454%	$117.8343	$117.83	$117.85	$117.80
Purchase #6	$194.28	7.276%	$208.4158	$208.42	$208.40	$208.40
Purchase #7	$168.98	7.809%	$182.1756	$182.18	$182.20	$182.20
7 purchase totals =	$1,005.03		$1,085.7272	$1,085.73	$1,085.80	$1,085.80