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	$170.30	12.445%	$191.4938	$191.49	$191.50	$191.50
Purchase #2	$222.70	12.508%	$250.5553	$250.56	$250.55	$250.60
Purchase #3	$181.53	4.176%	$189.1107	$189.11	$189.10	$189.10
Purchase #4	$83.65	8.132%	$90.4524	$90.45	$90.45	$90.50
Purchase #5	$103.80	10.623%	$114.8267	$114.83	$114.85	$114.80
Purchase #6	$208.70	9.317%	$228.1446	$228.14	$228.15	$228.10
Purchase #7	$37.33	12.376%	$41.95	$41.95	$41.95	$42.00
7 purchase totals =	$1,008.01		$1,106.5335	$1,106.53	$1,106.55	$1,106.60