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	$172.76	5.820%	$182.8146	$182.81	$182.80	$182.80
Purchase #2	$182.56	7.808%	$196.8143	$196.81	$196.80	$196.80
Purchase #3	$48.96	12.165%	$54.916	$54.92	$54.90	$54.90
Purchase #4	$242.67	8.848%	$264.1414	$264.14	$264.15	$264.10
Purchase #5	$173.77	3.109%	$179.1725	$179.17	$179.15	$179.20
Purchase #6	$163.82	7.298%	$175.7756	$175.78	$175.80	$175.80
Purchase #7	$17.35	13.574%	$19.7051	$19.71	$19.70	$19.70
7 purchase totals =	$1,001.89		$1,073.3395	$1,073.34	$1,073.30	$1,073.30