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	$173.93	13.563%	$197.5201	$197.52	$197.50	$197.50
Purchase #2	$138.81	9.531%	$152.04	$152.04	$152.05	$152.00
Purchase #3	$72.61	10.553%	$80.2725	$80.27	$80.25	$80.30
Purchase #4	$19.25	4.450%	$20.1066	$20.11	$20.10	$20.10
Purchase #5	$86.91	4.715%	$91.0078	$91.01	$91.00	$91.00
Purchase #6	$218.77	11.600%	$244.1473	$244.15	$244.15	$244.10
Purchase #7	$31.31	3.179%	$32.3053	$32.31	$32.30	$32.30
7 purchase totals =	$741.59		$817.3996	$817.41	$817.35	$817.30