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	$72.82	8.261%	$78.8357	$78.84	$78.85	$78.80
Purchase #2	$159.87	5.191%	$168.1689	$168.17	$168.15	$168.20
Purchase #3	$79.37	6.107%	$84.2171	$84.22	$84.20	$84.20
Purchase #4	$122.46	4.528%	$128.005	$128.01	$128.00	$128.00
Purchase #5	$38.51	12.198%	$43.2074	$43.21	$43.20	$43.20
Purchase #6	$52.55	6.844%	$56.1465	$56.15	$56.15	$56.10
Purchase #7	$209.55	11.327%	$233.2857	$233.29	$233.30	$233.30
7 purchase totals =	$735.13		$791.8663	$791.89	$791.85	$791.80