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	$87.30	12.851%	$98.5189	$98.52	$98.50	$98.50
Purchase #2	$114.64	7.390%	$123.1119	$123.11	$123.10	$123.10
Purchase #3	$114.91	5.192%	$120.8761	$120.88	$120.90	$120.90
Purchase #4	$145.44	11.470%	$162.122	$162.12	$162.10	$162.10
Purchase #5	$115.78	6.842%	$123.7017	$123.70	$123.70	$123.70
Purchase #6	$171.93	9.520%	$188.2977	$188.30	$188.30	$188.30
Purchase #7	$104.27	11.134%	$115.8794	$115.88	$115.90	$115.90
7 purchase totals =	$854.27		$932.5077	$932.51	$932.50	$932.50