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	$228.86	12.822%	$258.2044	$258.20	$258.20	$258.20
Purchase #2	$128.45	5.791%	$135.8885	$135.89	$135.90	$135.90
Purchase #3	$27.46	12.748%	$30.9606	$30.96	$30.95	$31.00
Purchase #4	$144.94	9.205%	$158.2817	$158.28	$158.30	$158.30
Purchase #5	$151.33	9.178%	$165.2191	$165.22	$165.20	$165.20
Purchase #6	$187.66	12.331%	$210.8004	$210.80	$210.80	$210.80
Purchase #7	$81.90	9.394%	$89.5937	$89.59	$89.60	$89.60
7 purchase totals =	$950.60		$1,048.9484	$1,048.94	$1,048.95	$1,049.00