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	$76.35	7.613%	$82.1625	$82.16	$82.15	$82.20
Purchase #2	$69.33	12.477%	$77.9803	$77.98	$78.00	$78.00
Purchase #3	$242.54	13.513%	$275.3144	$275.31	$275.30	$275.30
Purchase #4	$244.78	6.270%	$260.1277	$260.13	$260.15	$260.10
Purchase #5	$224.95	12.864%	$253.8876	$253.89	$253.90	$253.90
Purchase #6	$249.55	10.467%	$275.6704	$275.67	$275.65	$275.70
Purchase #7	$84.25	6.565%	$89.781	$89.78	$89.80	$89.80
7 purchase totals =	$1,191.75		$1,314.9239	$1,314.92	$1,314.95	$1,315.00