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	$45.88	3.603%	$47.5331	$47.53	$47.55	$47.50
Purchase #2	$197.31	10.552%	$218.1302	$218.13	$218.15	$218.10
Purchase #3	$187.99	5.338%	$198.0249	$198.02	$198.00	$198.00
Purchase #4	$139.40	6.465%	$148.4122	$148.41	$148.40	$148.40
Purchase #5	$41.65	13.191%	$47.1441	$47.14	$47.15	$47.10
Purchase #6	$67.66	5.647%	$71.4808	$71.48	$71.50	$71.50
Purchase #7	$79.97	12.177%	$89.7079	$89.71	$89.70	$89.70
7 purchase totals =	$759.86		$820.4332	$820.42	$820.45	$820.30