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	$170.58	12.412%	$191.7524	$191.75	$191.75	$191.80
Purchase #2	$34.67	5.460%	$36.563	$36.56	$36.55	$36.60
Purchase #3	$59.91	3.686%	$62.1183	$62.12	$62.10	$62.10
Purchase #4	$29.96	7.754%	$32.2831	$32.28	$32.30	$32.30
Purchase #5	$121.93	5.640%	$128.8069	$128.81	$128.80	$128.80
Purchase #6	$68.27	6.522%	$72.7226	$72.72	$72.70	$72.70
Purchase #7	$119.66	9.575%	$131.1174	$131.12	$131.10	$131.10
7 purchase totals =	$604.98		$655.3637	$655.36	$655.30	$655.40