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	$115.59	13.394%	$131.0721	$131.07	$131.05	$131.10
Purchase #2	$91.58	5.384%	$96.5107	$96.51	$96.50	$96.50
Purchase #3	$90.70	5.180%	$95.3983	$95.40	$95.40	$95.40
Purchase #4	$71.33	10.274%	$78.6584	$78.66	$78.65	$78.70
Purchase #5	$140.56	13.399%	$159.3936	$159.39	$159.40	$159.40
Purchase #6	$81.62	12.698%	$91.9841	$91.98	$92.00	$92.00
Purchase #7	$170.47	12.336%	$191.4992	$191.50	$191.50	$191.50
7 purchase totals =	$761.85		$844.5164	$844.51	$844.50	$844.60