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	$136.77	5.417%	$144.1788	$144.18	$144.20	$144.20
Purchase #2	$80.55	10.550%	$89.048	$89.05	$89.05	$89.00
Purchase #3	$102.67	8.326%	$111.2183	$111.22	$111.20	$111.20
Purchase #4	$73.78	3.687%	$76.5003	$76.50	$76.50	$76.50
Purchase #5	$147.30	12.344%	$165.4827	$165.48	$165.50	$165.50
Purchase #6	$183.62	4.415%	$191.7268	$191.73	$191.75	$191.70
Purchase #7	$66.80	10.463%	$73.7893	$73.79	$73.80	$73.80
7 purchase totals =	$791.49		$851.9442	$851.95	$852.00	$851.90