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	$180.85	4.678%	$189.3102	$189.31	$189.30	$189.30
Purchase #2	$157.87	4.725%	$165.3294	$165.33	$165.35	$165.30
Purchase #3	$108.45	6.375%	$115.3637	$115.36	$115.35	$115.40
Purchase #4	$39.71	12.300%	$44.5943	$44.59	$44.60	$44.60
Purchase #5	$52.59	8.281%	$56.945	$56.95	$56.95	$56.90
Purchase #6	$53.29	12.488%	$59.9449	$59.94	$59.95	$59.90
Purchase #7	$39.39	4.199%	$41.044	$41.04	$41.05	$41.00
7 purchase totals =	$632.15		$672.5315	$672.52	$672.55	$672.40