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	$33.86	10.673%	$37.4739	$37.47	$37.45	$37.50
Purchase #2	$42.78	8.726%	$46.513	$46.51	$46.50	$46.50
Purchase #3	$183.39	9.157%	$200.183	$200.18	$200.20	$200.20
Purchase #4	$11.80	12.753%	$13.3049	$13.30	$13.30	$13.30
Purchase #5	$54.38	8.744%	$59.135	$59.14	$59.15	$59.10
Purchase #6	$19.61	4.523%	$20.497	$20.50	$20.50	$20.50
Purchase #7	$243.54	12.145%	$273.1179	$273.12	$273.10	$273.10
7 purchase totals =	$589.36		$650.2247	$650.22	$650.20	$650.20