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	$129.97	8.433%	$140.9304	$140.93	$140.95	$140.90
Purchase #2	$111.96	7.452%	$120.3033	$120.30	$120.30	$120.30
Purchase #3	$169.39	7.334%	$181.8131	$181.81	$181.80	$181.80
Purchase #4	$104.78	12.740%	$118.129	$118.13	$118.15	$118.10
Purchase #5	$42.27	3.723%	$43.8437	$43.84	$43.85	$43.80
Purchase #6	$212.87	7.263%	$228.3307	$228.33	$228.35	$228.30
Purchase #7	$242.27	10.193%	$266.9646	$266.96	$266.95	$267.00
7 purchase totals =	$1,013.51		$1,100.3148	$1,100.30	$1,100.35	$1,100.20