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	$37.69	6.265%	$40.0513	$40.05	$40.05	$40.10
Purchase #2	$189.36	8.403%	$205.2719	$205.27	$205.25	$205.30
Purchase #3	$78.90	3.165%	$81.3972	$81.40	$81.40	$81.40
Purchase #4	$71.41	9.804%	$78.411	$78.41	$78.40	$78.40
Purchase #5	$181.27	12.677%	$204.2496	$204.25	$204.25	$204.20
Purchase #6	$194.44	12.305%	$218.3658	$218.37	$218.35	$218.40
Purchase #7	$6.29	4.666%	$6.5835	$6.58	$6.60	$6.60
7 purchase totals =	$759.36		$834.3303	$834.33	$834.30	$834.40