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	$117.58	11.428%	$131.017	$131.02	$131.00	$131.00
Purchase #2	$247.75	13.276%	$280.6413	$280.64	$280.65	$280.60
Purchase #3	$209.97	8.340%	$227.4815	$227.48	$227.50	$227.50
Purchase #4	$173.28	7.780%	$186.7612	$186.76	$186.75	$186.80
Purchase #5	$174.52	5.217%	$183.6247	$183.62	$183.60	$183.60
Purchase #6	$243.27	9.663%	$266.7772	$266.78	$266.80	$266.80
Purchase #7	$209.54	6.489%	$223.1371	$223.14	$223.15	$223.10
7 purchase totals =	$1,375.91		$1,499.4400	$1,499.44	$1,499.45	$1,499.40