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	$34.36	7.448%	$36.9191	$36.92	$36.90	$36.90
Purchase #2	$33.49	4.751%	$35.0811	$35.08	$35.10	$35.10
Purchase #3	$174.70	12.562%	$196.6458	$196.65	$196.65	$196.60
Purchase #4	$114.82	11.294%	$127.7878	$127.79	$127.80	$127.80
Purchase #5	$173.31	4.754%	$181.5492	$181.55	$181.55	$181.50
Purchase #6	$27.44	4.711%	$28.7327	$28.73	$28.75	$28.70
Purchase #7	$187.72	6.718%	$200.331	$200.33	$200.35	$200.30
7 purchase totals =	$745.84		$807.0467	$807.05	$807.10	$806.90