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	$28.46	8.278%	$30.8159	$30.82	$30.80	$30.80
Purchase #2	$86.68	11.146%	$96.3414	$96.34	$96.35	$96.30
Purchase #3	$67.26	8.169%	$72.7545	$72.75	$72.75	$72.80
Purchase #4	$96.33	7.405%	$103.4632	$103.46	$103.45	$103.50
Purchase #5	$130.40	10.385%	$143.942	$143.94	$143.95	$143.90
Purchase #6	$99.50	7.594%	$107.056	$107.06	$107.05	$107.10
Purchase #7	$89.73	6.417%	$95.488	$95.49	$95.50	$95.50
7 purchase totals =	$598.36		$649.8610	$649.86	$649.85	$649.90