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	$128.68	9.189%	$140.5044	$140.50	$140.50	$140.50
Purchase #2	$100.91	11.132%	$112.1433	$112.14	$112.15	$112.10
Purchase #3	$37.89	12.695%	$42.7001	$42.70	$42.70	$42.70
Purchase #4	$211.71	10.424%	$233.7787	$233.78	$233.80	$233.80
Purchase #5	$177.38	10.726%	$196.4058	$196.41	$196.40	$196.40
Purchase #6	$6.61	8.314%	$7.1596	$7.16	$7.15	$7.20
Purchase #7	$32.41	13.623%	$36.8252	$36.83	$36.85	$36.80
7 purchase totals =	$695.59		$769.5171	$769.52	$769.55	$769.50