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	$104.62	10.787%	$115.9054	$115.91	$115.90	$115.90
Purchase #2	$39.59	5.361%	$41.7124	$41.71	$41.70	$41.70
Purchase #3	$199.89	9.316%	$218.5118	$218.51	$218.50	$218.50
Purchase #4	$195.99	13.319%	$222.0939	$222.09	$222.10	$222.10
Purchase #5	$178.30	7.626%	$191.8972	$191.90	$191.90	$191.90
Purchase #6	$19.91	13.169%	$22.5319	$22.53	$22.55	$22.50
Purchase #7	$86.91	4.381%	$90.7175	$90.72	$90.70	$90.70
7 purchase totals =	$825.21		$903.3701	$903.37	$903.35	$903.30