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	$93.71	4.479%	$97.9073	$97.91	$97.90	$97.90
Purchase #2	$41.43	3.501%	$42.8805	$42.88	$42.90	$42.90
Purchase #3	$116.57	12.566%	$131.2182	$131.22	$131.20	$131.20
Purchase #4	$10.62	10.849%	$11.7722	$11.77	$11.75	$11.80
Purchase #5	$224.53	12.704%	$253.0543	$253.05	$253.05	$253.10
Purchase #6	$178.35	9.134%	$194.6405	$194.64	$194.65	$194.60
Purchase #7	$75.45	12.816%	$85.1197	$85.12	$85.10	$85.10
7 purchase totals =	$740.66		$816.5927	$816.59	$816.55	$816.60