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	$222.63	6.234%	$236.5088	$236.51	$236.50	$236.50
Purchase #2	$223.45	12.297%	$250.9276	$250.93	$250.95	$250.90
Purchase #3	$91.37	12.868%	$103.1275	$103.13	$103.15	$103.10
Purchase #4	$73.58	7.362%	$78.997	$79.00	$79.00	$79.00
Purchase #5	$107.41	10.293%	$118.4657	$118.47	$118.45	$118.50
Purchase #6	$250.69	11.799%	$280.2689	$280.27	$280.25	$280.30
Purchase #7	$95.90	10.700%	$106.1613	$106.16	$106.15	$106.20
7 purchase totals =	$1,065.03		$1,174.4568	$1,174.47	$1,174.45	$1,174.50