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	$90.50	6.533%	$96.4124	$96.41	$96.40	$96.40
Purchase #2	$94.26	6.221%	$100.1239	$100.12	$100.10	$100.10
Purchase #3	$236.78	13.580%	$268.9347	$268.93	$268.95	$268.90
Purchase #4	$20.72	13.600%	$23.5379	$23.54	$23.55	$23.50
Purchase #5	$28.48	6.485%	$30.3269	$30.33	$30.35	$30.30
Purchase #6	$92.61	12.850%	$104.5104	$104.51	$104.50	$104.50
Purchase #7	$42.93	13.245%	$48.6161	$48.62	$48.60	$48.60
7 purchase totals =	$606.28		$672.4623	$672.46	$672.45	$672.30