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	$11.89	7.301%	$12.7581	$12.76	$12.75	$12.80
Purchase #2	$92.33	13.595%	$104.8823	$104.88	$104.90	$104.90
Purchase #3	$211.46	13.267%	$239.5144	$239.51	$239.50	$239.50
Purchase #4	$238.42	5.135%	$250.6629	$250.66	$250.65	$250.70
Purchase #5	$141.41	3.144%	$145.8559	$145.86	$145.85	$145.90
Purchase #6	$51.36	5.719%	$54.2973	$54.30	$54.30	$54.30
Purchase #7	$205.76	8.856%	$223.9821	$223.98	$224.00	$224.00
7 purchase totals =	$952.63		$1,031.9530	$1,031.95	$1,031.95	$1,032.10