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	$37.81	11.520%	$42.1657	$42.17	$42.15	$42.20
Purchase #2	$22.52	13.292%	$25.5134	$25.51	$25.50	$25.50
Purchase #3	$158.93	9.802%	$174.5083	$174.51	$174.50	$174.50
Purchase #4	$175.46	8.760%	$190.8303	$190.83	$190.85	$190.80
Purchase #5	$181.47	9.869%	$199.3793	$199.38	$199.40	$199.40
Purchase #6	$59.47	12.768%	$67.0631	$67.06	$67.05	$67.10
Purchase #7	$123.75	9.260%	$135.2093	$135.21	$135.20	$135.20
7 purchase totals =	$759.41		$834.6694	$834.67	$834.65	$834.70