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	$158.33	12.281%	$177.7745	$177.77	$177.75	$177.80
Purchase #2	$78.69	6.147%	$83.5271	$83.53	$83.55	$83.50
Purchase #3	$74.64	3.480%	$77.2375	$77.24	$77.25	$77.20
Purchase #4	$139.50	9.332%	$152.5181	$152.52	$152.50	$152.50
Purchase #5	$45.31	6.581%	$48.2919	$48.29	$48.30	$48.30
Purchase #6	$89.25	8.155%	$96.5283	$96.53	$96.55	$96.50
Purchase #7	$150.60	3.840%	$156.383	$156.38	$156.40	$156.40
7 purchase totals =	$736.32		$792.2604	$792.26	$792.30	$792.20