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	$6.62	7.109%	$7.0906	$7.09	$7.10	$7.10
Purchase #2	$71.70	9.215%	$78.3072	$78.31	$78.30	$78.30
Purchase #3	$131.33	13.435%	$148.9742	$148.97	$148.95	$149.00
Purchase #4	$172.36	11.109%	$191.5075	$191.51	$191.50	$191.50
Purchase #5	$130.62	13.872%	$148.7396	$148.74	$148.75	$148.70
Purchase #6	$183.83	5.824%	$194.5363	$194.54	$194.55	$194.50
Purchase #7	$100.36	7.350%	$107.7365	$107.74	$107.75	$107.70
7 purchase totals =	$796.82		$876.8919	$876.90	$876.90	$876.80