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	$37.47	12.601%	$42.1916	$42.19	$42.20	$42.20
Purchase #2	$22.67	12.108%	$25.4149	$25.41	$25.40	$25.40
Purchase #3	$78.44	10.335%	$86.5468	$86.55	$86.55	$86.50
Purchase #4	$248.90	8.392%	$269.7877	$269.79	$269.80	$269.80
Purchase #5	$177.82	9.863%	$195.3584	$195.36	$195.35	$195.40
Purchase #6	$6.79	6.582%	$7.2369	$7.24	$7.25	$7.20
Purchase #7	$99.52	11.687%	$111.1509	$111.15	$111.15	$111.20
7 purchase totals =	$671.61		$737.6872	$737.69	$737.70	$737.70