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	$84.71	4.775%	$88.7549	$88.75	$88.75	$88.80
Purchase #2	$181.92	4.161%	$189.4897	$189.49	$189.50	$189.50
Purchase #3	$131.72	9.224%	$143.8699	$143.87	$143.85	$143.90
Purchase #4	$30.93	12.760%	$34.8767	$34.88	$34.90	$34.90
Purchase #5	$249.89	12.598%	$281.3711	$281.37	$281.35	$281.40
Purchase #6	$93.41	11.685%	$104.325	$104.33	$104.35	$104.30
Purchase #7	$86.96	4.834%	$91.1636	$91.16	$91.15	$91.20
7 purchase totals =	$859.54		$933.8509	$933.85	$933.85	$934.00