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	$46.73	12.314%	$52.4843	$52.48	$52.50	$52.50
Purchase #2	$156.70	8.518%	$170.0477	$170.05	$170.05	$170.00
Purchase #3	$197.75	6.559%	$210.7204	$210.72	$210.70	$210.70
Purchase #4	$243.47	13.246%	$275.72	$275.72	$275.70	$275.70
Purchase #5	$35.95	12.405%	$40.4096	$40.41	$40.40	$40.40
Purchase #6	$171.46	9.670%	$188.0402	$188.04	$188.05	$188.00
Purchase #7	$89.98	7.405%	$96.643	$96.64	$96.65	$96.60
7 purchase totals =	$942.04		$1,034.0652	$1,034.06	$1,034.05	$1,033.90