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	$101.80	5.606%	$107.5069	$107.51	$107.50	$107.50
Purchase #2	$64.51	7.460%	$69.3224	$69.32	$69.30	$69.30
Purchase #3	$236.54	13.432%	$268.3121	$268.31	$268.30	$268.30
Purchase #4	$47.51	3.140%	$49.0018	$49.00	$49.00	$49.00
Purchase #5	$102.97	13.778%	$117.1572	$117.16	$117.15	$117.20
Purchase #6	$88.67	12.256%	$99.5374	$99.54	$99.55	$99.50
Purchase #7	$98.32	11.479%	$109.6062	$109.61	$109.60	$109.60
7 purchase totals =	$740.32		$820.4440	$820.45	$820.40	$820.40