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	$47.38	11.493%	$52.8254	$52.83	$52.85	$52.80
Purchase #2	$152.70	10.689%	$169.0221	$169.02	$169.00	$169.00
Purchase #3	$176.98	9.575%	$193.9258	$193.93	$193.95	$193.90
Purchase #4	$30.47	8.580%	$33.0843	$33.08	$33.10	$33.10
Purchase #5	$81.55	11.680%	$91.075	$91.08	$91.10	$91.10
Purchase #6	$118.69	7.643%	$127.7615	$127.76	$127.75	$127.80
Purchase #7	$152.53	10.222%	$168.1216	$168.12	$168.10	$168.10
7 purchase totals =	$760.30		$835.8157	$835.82	$835.85	$835.80