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	$137.33	5.781%	$145.269	$145.27	$145.25	$145.30
Purchase #2	$19.56	13.872%	$22.2734	$22.27	$22.25	$22.30
Purchase #3	$247.52	6.336%	$263.2029	$263.20	$263.20	$263.20
Purchase #4	$56.90	10.356%	$62.7926	$62.79	$62.80	$62.80
Purchase #5	$94.48	9.328%	$103.2931	$103.29	$103.30	$103.30
Purchase #6	$70.85	10.496%	$78.2864	$78.29	$78.30	$78.30
Purchase #7	$113.33	13.488%	$128.616	$128.62	$128.60	$128.60
7 purchase totals =	$739.97		$803.7334	$803.73	$803.70	$803.80