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	$241.91	13.809%	$275.3154	$275.32	$275.30	$275.30
Purchase #2	$238.95	3.307%	$246.8521	$246.85	$246.85	$246.90
Purchase #3	$105.47	3.444%	$109.1024	$109.10	$109.10	$109.10
Purchase #4	$213.49	13.149%	$241.5618	$241.56	$241.55	$241.60
Purchase #5	$55.38	7.287%	$59.4155	$59.42	$59.40	$59.40
Purchase #6	$200.42	3.377%	$207.1882	$207.19	$207.20	$207.20
Purchase #7	$31.47	12.317%	$35.3462	$35.35	$35.35	$35.30
7 purchase totals =	$1,087.09		$1,174.7816	$1,174.79	$1,174.75	$1,174.80