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	$149.56	3.489%	$154.7781	$154.78	$154.80	$154.80
Purchase #2	$247.47	5.227%	$260.4053	$260.41	$260.40	$260.40
Purchase #3	$99.47	6.358%	$105.7943	$105.79	$105.80	$105.80
Purchase #4	$181.82	6.758%	$194.1074	$194.11	$194.10	$194.10
Purchase #5	$119.72	10.126%	$131.8428	$131.84	$131.85	$131.80
Purchase #6	$213.79	13.596%	$242.8569	$242.86	$242.85	$242.90
Purchase #7	$223.86	6.345%	$238.0639	$238.06	$238.05	$238.10
7 purchase totals =	$1,235.69		$1,327.8487	$1,327.85	$1,327.85	$1,327.90