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	$55.96	6.225%	$59.4435	$59.44	$59.45	$59.40
Purchase #2	$123.31	3.770%	$127.9588	$127.96	$127.95	$128.00
Purchase #3	$218.54	13.473%	$247.9839	$247.98	$248.00	$248.00
Purchase #4	$139.34	13.661%	$158.3752	$158.38	$158.40	$158.40
Purchase #5	$91.73	8.797%	$99.7995	$99.80	$99.80	$99.80
Purchase #6	$51.33	12.539%	$57.7663	$57.77	$57.75	$57.80
Purchase #7	$71.33	11.285%	$79.3796	$79.38	$79.40	$79.40
7 purchase totals =	$751.54		$830.7068	$830.71	$830.75	$830.80