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	$89.43	10.792%	$99.0813	$99.08	$99.10	$99.10
Purchase #2	$208.76	7.198%	$223.7865	$223.79	$223.80	$223.80
Purchase #3	$183.39	6.245%	$194.8427	$194.84	$194.85	$194.80
Purchase #4	$247.31	11.662%	$276.1513	$276.15	$276.15	$276.20
Purchase #5	$170.56	3.128%	$175.8951	$175.90	$175.90	$175.90
Purchase #6	$169.34	7.791%	$182.5333	$182.53	$182.55	$182.50
Purchase #7	$94.81	9.586%	$103.8985	$103.90	$103.90	$103.90
7 purchase totals =	$1,163.60		$1,256.1887	$1,256.19	$1,256.25	$1,256.20