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	$6.60	12.336%	$7.4142	$7.41	$7.40	$7.40
Purchase #2	$176.36	3.102%	$181.8307	$181.83	$181.85	$181.80
Purchase #3	$169.25	13.148%	$191.503	$191.50	$191.50	$191.50
Purchase #4	$250.64	5.111%	$263.4502	$263.45	$263.45	$263.50
Purchase #5	$74.54	11.626%	$83.206	$83.21	$83.20	$83.20
Purchase #6	$70.85	12.363%	$79.6092	$79.61	$79.60	$79.60
Purchase #7	$210.81	9.765%	$231.3956	$231.40	$231.40	$231.40
7 purchase totals =	$959.05		$1,038.4089	$1,038.41	$1,038.40	$1,038.40