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	$230.56	8.619%	$250.432	$250.43	$250.45	$250.40
Purchase #2	$205.75	8.766%	$223.786	$223.79	$223.80	$223.80
Purchase #3	$102.89	10.671%	$113.8694	$113.87	$113.85	$113.90
Purchase #4	$56.33	8.675%	$61.2166	$61.22	$61.20	$61.20
Purchase #5	$209.59	11.563%	$233.8249	$233.82	$233.80	$233.80
Purchase #6	$72.34	6.668%	$77.1636	$77.16	$77.15	$77.20
Purchase #7	$39.85	10.146%	$43.8932	$43.89	$43.90	$43.90
7 purchase totals =	$917.31		$1,004.1857	$1,004.18	$1,004.15	$1,004.20