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	$38.31	11.376%	$42.6681	$42.67	$42.65	$42.70
Purchase #2	$235.68	4.121%	$245.3924	$245.39	$245.40	$245.40
Purchase #3	$139.56	8.191%	$150.9914	$150.99	$151.00	$151.00
Purchase #4	$232.69	7.713%	$250.6374	$250.64	$250.65	$250.60
Purchase #5	$126.31	4.178%	$131.5872	$131.59	$131.60	$131.60
Purchase #6	$28.58	13.835%	$32.534	$32.53	$32.55	$32.50
Purchase #7	$18.96	6.742%	$20.2383	$20.24	$20.25	$20.20
7 purchase totals =	$820.09		$874.0488	$874.05	$874.10	$874.00