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	$83.77	5.699%	$88.5441	$88.54	$88.55	$88.50
Purchase #2	$158.30	13.604%	$179.8351	$179.84	$179.85	$179.80
Purchase #3	$33.35	6.221%	$35.4247	$35.42	$35.40	$35.40
Purchase #4	$181.38	12.367%	$203.8113	$203.81	$203.80	$203.80
Purchase #5	$217.34	3.517%	$224.9838	$224.98	$225.00	$225.00
Purchase #6	$80.55	13.266%	$91.2358	$91.24	$91.25	$91.20
Purchase #7	$187.92	4.361%	$196.1152	$196.12	$196.10	$196.10
7 purchase totals =	$942.61		$1,019.9500	$1,019.95	$1,019.95	$1,019.80