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	$38.36	4.615%	$40.1303	$40.13	$40.15	$40.10
Purchase #2	$134.94	3.644%	$139.8572	$139.86	$139.85	$139.90
Purchase #3	$60.52	11.251%	$67.3291	$67.33	$67.35	$67.30
Purchase #4	$73.41	7.419%	$78.8563	$78.86	$78.85	$78.90
Purchase #5	$131.88	7.136%	$141.291	$141.29	$141.30	$141.30
Purchase #6	$172.46	6.465%	$183.6095	$183.61	$183.60	$183.60
Purchase #7	$53.28	12.777%	$60.0876	$60.09	$60.10	$60.10
7 purchase totals =	$664.85		$711.1610	$711.17	$711.20	$711.20