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	$110.77	12.191%	$124.274	$124.27	$124.25	$124.30
Purchase #2	$13.90	12.391%	$15.6223	$15.62	$15.60	$15.60
Purchase #3	$40.44	3.575%	$41.8857	$41.89	$41.90	$41.90
Purchase #4	$82.67	12.552%	$93.0467	$93.05	$93.05	$93.00
Purchase #5	$184.64	3.304%	$190.7405	$190.74	$190.75	$190.70
Purchase #6	$71.34	9.824%	$78.3484	$78.35	$78.35	$78.30
Purchase #7	$250.56	10.479%	$276.8162	$276.82	$276.80	$276.80
7 purchase totals =	$754.32		$820.7338	$820.74	$820.70	$820.60