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	$134.32	10.233%	$148.065	$148.07	$148.05	$148.10
Purchase #2	$240.34	11.393%	$267.7219	$267.72	$267.70	$267.70
Purchase #3	$48.71	3.761%	$50.542	$50.54	$50.55	$50.50
Purchase #4	$84.49	8.403%	$91.5897	$91.59	$91.60	$91.60
Purchase #5	$61.77	11.107%	$68.6308	$68.63	$68.65	$68.60
Purchase #6	$82.90	6.621%	$88.3888	$88.39	$88.40	$88.40
Purchase #7	$53.80	10.669%	$59.5399	$59.54	$59.55	$59.50
7 purchase totals =	$706.33		$774.4781	$774.48	$774.50	$774.40