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	$90.93	8.336%	$98.5099	$98.51	$98.50	$98.50
Purchase #2	$51.43	12.341%	$57.777	$57.78	$57.80	$57.80
Purchase #3	$243.26	6.102%	$258.1037	$258.10	$258.10	$258.10
Purchase #4	$41.38	9.145%	$45.1642	$45.16	$45.15	$45.20
Purchase #5	$234.49	6.662%	$250.1117	$250.11	$250.10	$250.10
Purchase #6	$119.33	3.709%	$123.7559	$123.76	$123.75	$123.80
Purchase #7	$11.91	4.851%	$12.4878	$12.49	$12.50	$12.50
7 purchase totals =	$792.73		$845.9102	$845.91	$845.90	$846.00