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	$26.72	6.145%	$28.3619	$28.36	$28.35	$28.40
Purchase #2	$184.63	11.552%	$205.9585	$205.96	$205.95	$206.00
Purchase #3	$201.51	12.664%	$227.0292	$227.03	$227.05	$227.00
Purchase #4	$147.25	7.560%	$158.3821	$158.38	$158.40	$158.40
Purchase #5	$171.89	4.868%	$180.2576	$180.26	$180.25	$180.30
Purchase #6	$133.29	8.116%	$144.1078	$144.11	$144.10	$144.10
Purchase #7	$183.38	7.331%	$196.8236	$196.82	$196.80	$196.80
7 purchase totals =	$1,048.67		$1,140.9207	$1,140.92	$1,140.90	$1,141.00