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	$91.32	10.104%	$100.547	$100.55	$100.55	$100.50
Purchase #2	$87.72	10.302%	$96.7569	$96.76	$96.75	$96.80
Purchase #3	$219.41	4.638%	$229.5862	$229.59	$229.60	$229.60
Purchase #4	$65.48	10.356%	$72.2611	$72.26	$72.25	$72.30
Purchase #5	$8.47	5.140%	$8.9054	$8.91	$8.90	$8.90
Purchase #6	$135.94	12.247%	$152.5886	$152.59	$152.60	$152.60
Purchase #7	$5.84	5.251%	$6.1467	$6.15	$6.15	$6.10
7 purchase totals =	$614.18		$666.7919	$666.81	$666.80	$666.80