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	$168.53	13.531%	$191.3338	$191.33	$191.35	$191.30
Purchase #2	$157.41	4.849%	$165.0428	$165.04	$165.05	$165.00
Purchase #3	$40.90	6.341%	$43.4935	$43.49	$43.50	$43.50
Purchase #4	$72.39	11.693%	$80.8546	$80.85	$80.85	$80.90
Purchase #5	$161.45	13.836%	$183.7882	$183.79	$183.80	$183.80
Purchase #6	$60.90	3.125%	$62.8031	$62.80	$62.80	$62.80
Purchase #7	$73.95	12.386%	$83.1094	$83.11	$83.10	$83.10
7 purchase totals =	$735.53		$810.4254	$810.41	$810.45	$810.40