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	$131.50	11.654%	$146.825	$146.83	$146.85	$146.80
Purchase #2	$85.33	8.343%	$92.4491	$92.45	$92.45	$92.40
Purchase #3	$89.74	12.832%	$101.2554	$101.26	$101.25	$101.30
Purchase #4	$197.76	3.311%	$204.3078	$204.31	$204.30	$204.30
Purchase #5	$12.34	4.656%	$12.9146	$12.91	$12.90	$12.90
Purchase #6	$158.89	4.688%	$166.3388	$166.34	$166.35	$166.30
Purchase #7	$176.31	10.229%	$194.3447	$194.34	$194.35	$194.30
7 purchase totals =	$851.87		$918.4354	$918.44	$918.45	$918.30