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	$50.56	10.560%	$55.8991	$55.90	$55.90	$55.90
Purchase #2	$161.28	8.340%	$174.7308	$174.73	$174.75	$174.70
Purchase #3	$209.33	7.713%	$225.4756	$225.48	$225.50	$225.50
Purchase #4	$79.39	3.489%	$82.1599	$82.16	$82.15	$82.20
Purchase #5	$140.30	12.325%	$157.592	$157.59	$157.60	$157.60
Purchase #6	$215.34	12.697%	$242.6817	$242.68	$242.70	$242.70
Purchase #7	$48.34	5.360%	$50.931	$50.93	$50.95	$50.90
7 purchase totals =	$904.54		$989.4701	$989.47	$989.55	$989.50