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	$210.49	13.476%	$238.8556	$238.86	$238.85	$238.90
Purchase #2	$234.72	9.340%	$256.6428	$256.64	$256.65	$256.60
Purchase #3	$167.27	12.579%	$188.3109	$188.31	$188.30	$188.30
Purchase #4	$227.68	6.841%	$243.2556	$243.26	$243.25	$243.30
Purchase #5	$168.65	8.270%	$182.5974	$182.60	$182.60	$182.60
Purchase #6	$104.94	13.325%	$118.9233	$118.92	$118.90	$118.90
Purchase #7	$185.89	6.596%	$198.1513	$198.15	$198.15	$198.20
7 purchase totals =	$1,299.64		$1,426.7369	$1,426.74	$1,426.70	$1,426.80