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	$111.48	6.139%	$118.3238	$118.32	$118.30	$118.30
Purchase #2	$237.85	9.635%	$260.7668	$260.77	$260.75	$260.80
Purchase #3	$37.53	4.699%	$39.2935	$39.29	$39.30	$39.30
Purchase #4	$236.51	13.619%	$268.7203	$268.72	$268.70	$268.70
Purchase #5	$223.64	4.421%	$233.5271	$233.53	$233.55	$233.50
Purchase #6	$85.94	4.365%	$89.6913	$89.69	$89.70	$89.70
Purchase #7	$194.88	4.377%	$203.4099	$203.41	$203.40	$203.40
7 purchase totals =	$1,127.83		$1,213.7327	$1,213.73	$1,213.70	$1,213.70