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	$54.83	9.206%	$59.8776	$59.88	$59.90	$59.90
Purchase #2	$96.55	13.122%	$109.2193	$109.22	$109.20	$109.20
Purchase #3	$53.51	6.589%	$57.0358	$57.04	$57.05	$57.00
Purchase #4	$79.53	4.283%	$82.9363	$82.94	$82.95	$82.90
Purchase #5	$143.86	3.380%	$148.7225	$148.72	$148.70	$148.70
Purchase #6	$241.81	13.730%	$275.0105	$275.01	$275.00	$275.00
Purchase #7	$241.37	13.111%	$273.016	$273.02	$273.00	$273.00
7 purchase totals =	$911.46		$1,005.8180	$1,005.83	$1,005.80	$1,005.70