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	$65.33	7.354%	$70.1344	$70.13	$70.15	$70.10
Purchase #2	$155.90	8.326%	$168.8802	$168.88	$168.90	$168.90
Purchase #3	$148.61	8.316%	$160.9684	$160.97	$160.95	$161.00
Purchase #4	$110.82	13.331%	$125.5934	$125.59	$125.60	$125.60
Purchase #5	$53.71	10.438%	$59.3162	$59.32	$59.30	$59.30
Purchase #6	$42.65	13.365%	$48.3502	$48.35	$48.35	$48.40
Purchase #7	$69.91	3.113%	$72.0863	$72.09	$72.10	$72.10
7 purchase totals =	$646.93		$705.3291	$705.33	$705.35	$705.40