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	$147.31	8.367%	$159.6354	$159.64	$159.65	$159.60
Purchase #2	$222.28	8.111%	$240.3091	$240.31	$240.30	$240.30
Purchase #3	$156.90	10.217%	$172.9305	$172.93	$172.95	$172.90
Purchase #4	$68.41	4.492%	$71.483	$71.48	$71.50	$71.50
Purchase #5	$170.69	11.462%	$190.2545	$190.25	$190.25	$190.30
Purchase #6	$228.71	13.588%	$259.7871	$259.79	$259.80	$259.80
Purchase #7	$117.94	5.701%	$124.6638	$124.66	$124.65	$124.70
7 purchase totals =	$1,112.24		$1,219.0634	$1,219.06	$1,219.10	$1,219.10