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	$19.87	5.356%	$20.9342	$20.93	$20.95	$20.90
Purchase #2	$237.46	5.393%	$250.2662	$250.27	$250.25	$250.30
Purchase #3	$179.57	6.841%	$191.8544	$191.85	$191.85	$191.90
Purchase #4	$232.51	13.207%	$263.2176	$263.22	$263.20	$263.20
Purchase #5	$193.25	12.325%	$217.0681	$217.07	$217.05	$217.10
Purchase #6	$166.54	3.229%	$171.9176	$171.92	$171.90	$171.90
Purchase #7	$83.90	13.623%	$95.3297	$95.33	$95.35	$95.30
7 purchase totals =	$1,113.10		$1,210.5878	$1,210.59	$1,210.55	$1,210.60