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	$182.52	5.535%	$192.6225	$192.62	$192.60	$192.60
Purchase #2	$84.85	5.328%	$89.3708	$89.37	$89.35	$89.40
Purchase #3	$6.88	13.700%	$7.8226	$7.82	$7.80	$7.80
Purchase #4	$130.48	11.764%	$145.8297	$145.83	$145.85	$145.80
Purchase #5	$24.69	10.534%	$27.2908	$27.29	$27.30	$27.30
Purchase #6	$157.86	7.570%	$169.81	$169.81	$169.80	$169.80
Purchase #7	$25.53	9.663%	$27.997	$28.00	$28.00	$28.00
7 purchase totals =	$612.81		$660.7434	$660.74	$660.70	$660.70