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	$85.42	4.178%	$88.9888	$88.99	$89.00	$89.00
Purchase #2	$169.64	7.627%	$182.5784	$182.58	$182.60	$182.60
Purchase #3	$75.73	12.741%	$85.3788	$85.38	$85.40	$85.40
Purchase #4	$221.92	9.626%	$243.282	$243.28	$243.30	$243.30
Purchase #5	$54.76	5.244%	$57.6316	$57.63	$57.65	$57.60
Purchase #6	$36.90	6.472%	$39.2882	$39.29	$39.30	$39.30
Purchase #7	$168.60	10.234%	$185.8545	$185.85	$185.85	$185.90
7 purchase totals =	$812.97		$883.0023	$883.00	$883.10	$883.10