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	$68.90	5.810%	$72.9031	$72.90	$72.90	$72.90
Purchase #2	$144.94	9.510%	$158.7238	$158.72	$158.70	$158.70
Purchase #3	$235.41	9.179%	$257.0183	$257.02	$257.00	$257.00
Purchase #4	$38.75	6.179%	$41.1444	$41.14	$41.15	$41.10
Purchase #5	$124.44	5.471%	$131.2481	$131.25	$131.25	$131.20
Purchase #6	$119.56	3.328%	$123.539	$123.54	$123.55	$123.50
Purchase #7	$109.62	9.829%	$120.3945	$120.39	$120.40	$120.40
7 purchase totals =	$841.62		$904.9712	$904.96	$904.95	$904.80