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	$152.35	13.427%	$172.806	$172.81	$172.80	$172.80
Purchase #2	$198.43	6.384%	$211.0978	$211.10	$211.10	$211.10
Purchase #3	$75.34	9.871%	$82.7768	$82.78	$82.80	$82.80
Purchase #4	$19.55	8.840%	$21.2782	$21.28	$21.30	$21.30
Purchase #5	$64.53	6.663%	$68.8296	$68.83	$68.85	$68.80
Purchase #6	$106.59	4.565%	$111.4558	$111.46	$111.45	$111.50
Purchase #7	$77.56	7.106%	$83.0714	$83.07	$83.05	$83.10
7 purchase totals =	$694.35		$751.3156	$751.33	$751.35	$751.40