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	$28.83	11.655%	$32.1901	$32.19	$32.20	$32.20
Purchase #2	$105.50	12.284%	$118.4596	$118.46	$118.45	$118.50
Purchase #3	$192.49	12.360%	$216.2818	$216.28	$216.30	$216.30
Purchase #4	$196.42	13.160%	$222.2689	$222.27	$222.25	$222.30
Purchase #5	$180.71	13.832%	$205.7058	$205.71	$205.70	$205.70
Purchase #6	$59.90	6.797%	$63.9714	$63.97	$63.95	$64.00
Purchase #7	$57.70	11.632%	$64.4117	$64.41	$64.40	$64.40
7 purchase totals =	$821.55		$923.2893	$923.29	$923.25	$923.40