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	$18.89	6.649%	$20.146	$20.15	$20.15	$20.10
Purchase #2	$101.96	3.227%	$105.2502	$105.25	$105.25	$105.30
Purchase #3	$67.92	7.357%	$72.9169	$72.92	$72.90	$72.90
Purchase #4	$196.74	12.384%	$221.1043	$221.10	$221.10	$221.10
Purchase #5	$189.47	3.379%	$195.8722	$195.87	$195.85	$195.90
Purchase #6	$249.58	12.687%	$281.2442	$281.24	$281.25	$281.20
Purchase #7	$100.75	12.846%	$113.6923	$113.69	$113.70	$113.70
7 purchase totals =	$925.31		$1,010.2261	$1,010.22	$1,010.20	$1,010.20