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	$56.66	4.676%	$59.3094	$59.31	$59.30	$59.30
Purchase #2	$196.85	10.803%	$218.1157	$218.12	$218.10	$218.10
Purchase #3	$177.58	11.703%	$198.3622	$198.36	$198.35	$198.40
Purchase #4	$244.69	7.773%	$263.7098	$263.71	$263.70	$263.70
Purchase #5	$92.34	12.185%	$103.5916	$103.59	$103.60	$103.60
Purchase #6	$28.44	13.819%	$32.3701	$32.37	$32.35	$32.40
Purchase #7	$91.91	3.161%	$94.8153	$94.82	$94.80	$94.80
7 purchase totals =	$888.47		$970.2741	$970.28	$970.20	$970.30