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	$238.39	13.199%	$269.8551	$269.86	$269.85	$269.90
Purchase #2	$35.89	13.220%	$40.6347	$40.63	$40.65	$40.60
Purchase #3	$115.32	12.771%	$130.0475	$130.05	$130.05	$130.00
Purchase #4	$39.56	5.461%	$41.7204	$41.72	$41.70	$41.70
Purchase #5	$176.74	11.409%	$196.9043	$196.90	$196.90	$196.90
Purchase #6	$73.57	5.499%	$77.6156	$77.62	$77.60	$77.60
Purchase #7	$65.92	6.402%	$70.1402	$70.14	$70.15	$70.10
7 purchase totals =	$745.39		$826.9178	$826.92	$826.90	$826.80