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	$28.95	7.450%	$31.1068	$31.11	$31.10	$31.10
Purchase #2	$41.56	10.256%	$45.8224	$45.82	$45.80	$45.80
Purchase #3	$45.93	11.808%	$51.3534	$51.35	$51.35	$51.40
Purchase #4	$72.61	9.593%	$79.5755	$79.58	$79.60	$79.60
Purchase #5	$150.68	13.440%	$170.9314	$170.93	$170.95	$170.90
Purchase #6	$80.28	11.254%	$89.3147	$89.31	$89.30	$89.30
Purchase #7	$53.31	3.417%	$55.1316	$55.13	$55.15	$55.10
7 purchase totals =	$473.32		$523.2358	$523.23	$523.25	$523.20