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	$103.33	6.117%	$109.6507	$109.65	$109.65	$109.70
Purchase #2	$135.69	13.247%	$153.6649	$153.66	$153.65	$153.70
Purchase #3	$63.53	6.611%	$67.73	$67.73	$67.75	$67.70
Purchase #4	$111.85	10.357%	$123.4343	$123.43	$123.45	$123.40
Purchase #5	$25.62	7.603%	$27.5679	$27.57	$27.55	$27.60
Purchase #6	$103.98	7.186%	$111.452	$111.45	$111.45	$111.50
Purchase #7	$184.63	7.392%	$198.2778	$198.28	$198.30	$198.30
7 purchase totals =	$728.63		$791.7776	$791.77	$791.80	$791.90