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	$10.27	4.354%	$10.7172	$10.72	$10.70	$10.70
Purchase #2	$80.71	10.324%	$89.0425	$89.04	$89.05	$89.00
Purchase #3	$221.54	3.694%	$229.7237	$229.72	$229.70	$229.70
Purchase #4	$17.72	5.812%	$18.7499	$18.75	$18.75	$18.70
Purchase #5	$126.85	10.690%	$140.4103	$140.41	$140.40	$140.40
Purchase #6	$107.56	10.825%	$119.2034	$119.20	$119.20	$119.20
Purchase #7	$162.27	5.832%	$171.7336	$171.73	$171.75	$171.70
7 purchase totals =	$726.92		$779.5806	$779.57	$779.55	$779.40