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	$237.34	6.309%	$252.3138	$252.31	$252.30	$252.30
Purchase #2	$223.57	6.315%	$237.6884	$237.69	$237.70	$237.70
Purchase #3	$233.38	4.360%	$243.5554	$243.56	$243.55	$243.60
Purchase #4	$150.32	12.484%	$169.0859	$169.09	$169.10	$169.10
Purchase #5	$40.74	9.339%	$44.5447	$44.54	$44.55	$44.50
Purchase #6	$55.45	9.847%	$60.9102	$60.91	$60.90	$60.90
Purchase #7	$71.63	9.393%	$78.3582	$78.36	$78.35	$78.40
7 purchase totals =	$1,012.43		$1,086.4566	$1,086.46	$1,086.45	$1,086.50