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	$70.51	11.496%	$78.6158	$78.62	$78.60	$78.60
Purchase #2	$104.67	3.304%	$108.1283	$108.13	$108.15	$108.10
Purchase #3	$64.94	8.478%	$70.4456	$70.45	$70.45	$70.40
Purchase #4	$52.77	5.709%	$55.7826	$55.78	$55.80	$55.80
Purchase #5	$225.54	13.650%	$256.3262	$256.33	$256.35	$256.30
Purchase #6	$189.40	12.778%	$213.6015	$213.60	$213.60	$213.60
Purchase #7	$249.93	5.275%	$263.1138	$263.11	$263.10	$263.10
7 purchase totals =	$957.76		$1,046.0138	$1,046.02	$1,046.05	$1,045.90