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	$27.36	9.371%	$29.9239	$29.92	$29.90	$29.90
Purchase #2	$131.26	9.829%	$144.1615	$144.16	$144.15	$144.20
Purchase #3	$138.79	9.794%	$152.3831	$152.38	$152.40	$152.40
Purchase #4	$191.77	13.223%	$217.1277	$217.13	$217.15	$217.10
Purchase #5	$177.79	12.830%	$200.6005	$200.60	$200.60	$200.60
Purchase #6	$228.46	6.500%	$243.3099	$243.31	$243.30	$243.30
Purchase #7	$35.50	10.648%	$39.28	$39.28	$39.30	$39.30
7 purchase totals =	$930.93		$1,026.7866	$1,026.78	$1,026.80	$1,026.80