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	$198.44	3.593%	$205.5699	$205.57	$205.55	$205.60
Purchase #2	$220.38	10.311%	$243.1034	$243.10	$243.10	$243.10
Purchase #3	$138.72	9.681%	$152.1495	$152.15	$152.15	$152.10
Purchase #4	$53.73	10.382%	$59.3082	$59.31	$59.30	$59.30
Purchase #5	$17.69	3.671%	$18.3394	$18.34	$18.35	$18.30
Purchase #6	$101.53	10.110%	$111.7947	$111.79	$111.80	$111.80
Purchase #7	$126.34	3.117%	$130.278	$130.28	$130.30	$130.30
7 purchase totals =	$856.83		$920.5431	$920.54	$920.55	$920.50