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	$72.46	8.695%	$78.7604	$78.76	$78.75	$78.80
Purchase #2	$88.68	12.516%	$99.7792	$99.78	$99.80	$99.80
Purchase #3	$176.79	12.469%	$198.8339	$198.83	$198.85	$198.80
Purchase #4	$72.70	10.838%	$80.5792	$80.58	$80.60	$80.60
Purchase #5	$28.31	10.154%	$31.1846	$31.18	$31.20	$31.20
Purchase #6	$170.69	9.433%	$186.7912	$186.79	$186.80	$186.80
Purchase #7	$229.92	5.584%	$242.7587	$242.76	$242.75	$242.80
7 purchase totals =	$839.55		$918.6872	$918.68	$918.75	$918.80