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	$30.32	6.653%	$32.3372	$32.34	$32.35	$32.30
Purchase #2	$116.32	12.229%	$130.5448	$130.54	$130.55	$130.50
Purchase #3	$91.48	5.718%	$96.7108	$96.71	$96.70	$96.70
Purchase #4	$60.44	6.121%	$64.1395	$64.14	$64.15	$64.10
Purchase #5	$124.72	9.801%	$136.9438	$136.94	$136.95	$136.90
Purchase #6	$56.70	5.572%	$59.8593	$59.86	$59.85	$59.90
Purchase #7	$76.91	8.357%	$83.3374	$83.34	$83.35	$83.30
7 purchase totals =	$556.89		$603.8728	$603.87	$603.90	$603.70