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	$220.28	4.322%	$229.8005	$229.80	$229.80	$229.80
Purchase #2	$82.92	8.187%	$89.7087	$89.71	$89.70	$89.70
Purchase #3	$137.39	7.666%	$147.9223	$147.92	$147.90	$147.90
Purchase #4	$158.96	8.396%	$172.3063	$172.31	$172.30	$172.30
Purchase #5	$7.29	9.149%	$7.957	$7.96	$7.95	$8.00
Purchase #6	$75.54	10.282%	$83.307	$83.31	$83.30	$83.30
Purchase #7	$70.44	9.751%	$77.3086	$77.31	$77.30	$77.30
7 purchase totals =	$752.82		$808.3104	$808.32	$808.25	$808.30