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	$12.46	6.116%	$13.2221	$13.22	$13.20	$13.20
Purchase #2	$55.58	3.322%	$57.4264	$57.43	$57.45	$57.40
Purchase #3	$61.95	9.526%	$67.8514	$67.85	$67.85	$67.90
Purchase #4	$107.32	5.110%	$112.8041	$112.80	$112.80	$112.80
Purchase #5	$180.98	5.835%	$191.5402	$191.54	$191.55	$191.50
Purchase #6	$237.27	5.707%	$250.811	$250.81	$250.80	$250.80
Purchase #7	$37.61	8.767%	$40.9073	$40.91	$40.90	$40.90
7 purchase totals =	$693.17		$734.5625	$734.56	$734.55	$734.50