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	$46.55	11.458%	$51.8837	$51.88	$51.90	$51.90
Purchase #2	$61.95	10.511%	$68.4616	$68.46	$68.45	$68.50
Purchase #3	$70.77	11.371%	$78.8173	$78.82	$78.80	$78.80
Purchase #4	$235.69	3.327%	$243.5314	$243.53	$243.55	$243.50
Purchase #5	$154.57	13.581%	$175.5622	$175.56	$175.55	$175.60
Purchase #6	$160.66	13.843%	$182.9002	$182.90	$182.90	$182.90
Purchase #7	$208.42	3.220%	$215.1311	$215.13	$215.15	$215.10
7 purchase totals =	$938.61		$1,016.2875	$1,016.28	$1,016.30	$1,016.30