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	$244.83	11.397%	$272.7333	$272.73	$272.75	$272.70
Purchase #2	$88.55	12.667%	$99.7666	$99.77	$99.75	$99.80
Purchase #3	$219.66	10.465%	$242.6474	$242.65	$242.65	$242.60
Purchase #4	$60.32	11.465%	$67.2357	$67.24	$67.25	$67.20
Purchase #5	$78.27	5.849%	$82.848	$82.85	$82.85	$82.80
Purchase #6	$209.39	13.740%	$238.1602	$238.16	$238.15	$238.20
Purchase #7	$5.76	8.503%	$6.2498	$6.25	$6.25	$6.20
7 purchase totals =	$906.78		$1,009.6410	$1,009.65	$1,009.65	$1,009.50