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	$54.31	10.298%	$59.9028	$59.90	$59.90	$59.90
Purchase #2	$34.55	13.799%	$39.3176	$39.32	$39.30	$39.30
Purchase #3	$38.48	9.556%	$42.1571	$42.16	$42.15	$42.20
Purchase #4	$191.91	10.634%	$212.3177	$212.32	$212.30	$212.30
Purchase #5	$203.25	3.299%	$209.9552	$209.96	$209.95	$210.00
Purchase #6	$31.64	8.522%	$34.3364	$34.34	$34.35	$34.30
Purchase #7	$211.27	13.648%	$240.1041	$240.10	$240.10	$240.10
7 purchase totals =	$765.41		$838.0909	$838.10	$838.05	$838.10