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	$132.27	11.751%	$147.813	$147.81	$147.80	$147.80
Purchase #2	$215.78	5.705%	$228.0902	$228.09	$228.10	$228.10
Purchase #3	$229.64	7.322%	$246.4542	$246.45	$246.45	$246.50
Purchase #4	$20.78	10.161%	$22.8915	$22.89	$22.90	$22.90
Purchase #5	$191.62	12.586%	$215.7373	$215.74	$215.75	$215.70
Purchase #6	$73.46	6.779%	$78.4399	$78.44	$78.45	$78.40
Purchase #7	$56.76	11.610%	$63.3498	$63.35	$63.35	$63.30
7 purchase totals =	$920.31		$1,002.7759	$1,002.77	$1,002.80	$1,002.70