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	$116.51	12.494%	$131.0668	$131.07	$131.05	$131.10
Purchase #2	$203.78	3.653%	$211.2241	$211.22	$211.20	$211.20
Purchase #3	$237.31	4.678%	$248.4114	$248.41	$248.40	$248.40
Purchase #4	$32.76	13.768%	$37.2704	$37.27	$37.25	$37.30
Purchase #5	$51.57	8.269%	$55.8343	$55.83	$55.85	$55.80
Purchase #6	$104.52	4.631%	$109.3603	$109.36	$109.35	$109.40
Purchase #7	$175.71	12.818%	$198.2325	$198.23	$198.25	$198.20
7 purchase totals =	$922.16		$991.3998	$991.39	$991.35	$991.40