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	$238.64	6.585%	$254.3544	$254.35	$254.35	$254.40
Purchase #2	$235.78	12.440%	$265.111	$265.11	$265.10	$265.10
Purchase #3	$87.48	13.604%	$99.3808	$99.38	$99.40	$99.40
Purchase #4	$117.76	13.872%	$134.0957	$134.10	$134.10	$134.10
Purchase #5	$184.76	4.411%	$192.9098	$192.91	$192.90	$192.90
Purchase #6	$94.37	3.118%	$97.3125	$97.31	$97.30	$97.30
Purchase #7	$95.59	3.144%	$98.5953	$98.60	$98.60	$98.60
7 purchase totals =	$1,054.38		$1,141.7595	$1,141.76	$1,141.75	$1,141.80