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	$96.31	5.564%	$101.6687	$101.67	$101.65	$101.70
Purchase #2	$160.72	11.759%	$179.6191	$179.62	$179.60	$179.60
Purchase #3	$107.42	6.109%	$113.9823	$113.98	$114.00	$114.00
Purchase #4	$149.26	12.792%	$168.3533	$168.35	$168.35	$168.40
Purchase #5	$71.91	13.301%	$81.4747	$81.47	$81.45	$81.50
Purchase #6	$81.41	13.612%	$92.4915	$92.49	$92.50	$92.50
Purchase #7	$162.86	13.797%	$185.3298	$185.33	$185.35	$185.30
7 purchase totals =	$829.89		$922.9194	$922.91	$922.90	$923.00