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	$147.73	13.458%	$167.6115	$167.61	$167.60	$167.60
Purchase #2	$164.29	4.261%	$171.2904	$171.29	$171.30	$171.30
Purchase #3	$89.26	12.178%	$100.1301	$100.13	$100.15	$100.10
Purchase #4	$200.40	13.221%	$226.8949	$226.89	$226.90	$226.90
Purchase #5	$94.48	10.381%	$104.288	$104.29	$104.30	$104.30
Purchase #6	$30.31	12.402%	$34.069	$34.07	$34.05	$34.10
Purchase #7	$168.71	10.275%	$186.045	$186.05	$186.05	$186.00
7 purchase totals =	$895.18		$990.3289	$990.33	$990.35	$990.30