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	$92.57	8.337%	$100.2876	$100.29	$100.30	$100.30
Purchase #2	$220.92	12.513%	$248.5637	$248.56	$248.55	$248.60
Purchase #3	$241.94	13.497%	$274.5946	$274.59	$274.60	$274.60
Purchase #4	$53.82	13.663%	$61.1734	$61.17	$61.15	$61.20
Purchase #5	$144.88	10.369%	$159.9026	$159.90	$159.90	$159.90
Purchase #6	$69.33	11.611%	$77.3799	$77.38	$77.40	$77.40
Purchase #7	$200.51	3.197%	$206.9203	$206.92	$206.90	$206.90
7 purchase totals =	$1,023.97		$1,128.8221	$1,128.81	$1,128.80	$1,128.90