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	$225.64	6.414%	$240.1125	$240.11	$240.10	$240.10
Purchase #2	$128.61	10.266%	$141.8131	$141.81	$141.80	$141.80
Purchase #3	$39.70	6.298%	$42.2003	$42.20	$42.20	$42.20
Purchase #4	$196.79	9.313%	$215.1171	$215.12	$215.10	$215.10
Purchase #5	$62.53	8.286%	$67.7112	$67.71	$67.70	$67.70
Purchase #6	$127.53	4.271%	$132.9768	$132.98	$133.00	$133.00
Purchase #7	$219.76	10.262%	$242.3118	$242.31	$242.30	$242.30
7 purchase totals =	$1,000.56		$1,082.2428	$1,082.24	$1,082.20	$1,082.20