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	$37.37	5.704%	$39.5016	$39.50	$39.50	$39.50
Purchase #2	$221.78	5.257%	$233.439	$233.44	$233.45	$233.40
Purchase #3	$64.30	10.729%	$71.1987	$71.20	$71.20	$71.20
Purchase #4	$98.94	11.495%	$110.3132	$110.31	$110.30	$110.30
Purchase #5	$86.47	4.322%	$90.2072	$90.21	$90.20	$90.20
Purchase #6	$146.47	7.503%	$157.4596	$157.46	$157.45	$157.50
Purchase #7	$245.81	10.185%	$270.8457	$270.85	$270.85	$270.80
7 purchase totals =	$901.14		$972.9650	$972.97	$972.95	$972.90