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	$180.93	12.571%	$203.6747	$203.67	$203.65	$203.70
Purchase #2	$99.49	5.263%	$104.7262	$104.73	$104.75	$104.70
Purchase #3	$191.77	10.286%	$211.4955	$211.50	$211.50	$211.50
Purchase #4	$96.91	6.596%	$103.3022	$103.30	$103.30	$103.30
Purchase #5	$199.80	3.561%	$206.9149	$206.91	$206.90	$206.90
Purchase #6	$106.53	9.491%	$116.6408	$116.64	$116.65	$116.60
Purchase #7	$51.46	8.460%	$55.8135	$55.81	$55.80	$55.80
7 purchase totals =	$926.89		$1,002.5678	$1,002.56	$1,002.55	$1,002.50