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	$170.46	11.315%	$189.7475	$189.75	$189.75	$189.70
Purchase #2	$59.76	8.543%	$64.8653	$64.87	$64.85	$64.90
Purchase #3	$144.29	4.529%	$150.8249	$150.82	$150.80	$150.80
Purchase #4	$202.75	10.234%	$223.4994	$223.50	$223.50	$223.50
Purchase #5	$87.95	9.171%	$96.0159	$96.02	$96.00	$96.00
Purchase #6	$42.69	12.648%	$48.0894	$48.09	$48.10	$48.10
Purchase #7	$25.90	10.396%	$28.5926	$28.59	$28.60	$28.60
7 purchase totals =	$733.80		$801.6350	$801.64	$801.60	$801.60