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	$178.29	3.753%	$184.9812	$184.98	$185.00	$185.00
Purchase #2	$130.56	9.175%	$142.5389	$142.54	$142.55	$142.50
Purchase #3	$194.53	7.618%	$209.3493	$209.35	$209.35	$209.30
Purchase #4	$104.58	13.629%	$118.8332	$118.83	$118.85	$118.80
Purchase #5	$240.47	7.428%	$258.3321	$258.33	$258.35	$258.30
Purchase #6	$99.65	9.352%	$108.9693	$108.97	$108.95	$109.00
Purchase #7	$179.77	11.153%	$199.8197	$199.82	$199.80	$199.80
7 purchase totals =	$1,127.85		$1,222.8237	$1,222.82	$1,222.85	$1,222.70