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	$249.34	10.232%	$274.8525	$274.85	$274.85	$274.90
Purchase #2	$249.31	7.631%	$268.3348	$268.33	$268.35	$268.30
Purchase #3	$123.58	11.513%	$137.8078	$137.81	$137.80	$137.80
Purchase #4	$120.89	4.640%	$126.4993	$126.50	$126.50	$126.50
Purchase #5	$141.34	4.392%	$147.5477	$147.55	$147.55	$147.50
Purchase #6	$225.83	13.774%	$256.9358	$256.94	$256.95	$256.90
Purchase #7	$248.88	6.273%	$264.4922	$264.49	$264.50	$264.50
7 purchase totals =	$1,359.17		$1,476.4701	$1,476.47	$1,476.50	$1,476.40