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	$116.89	12.315%	$131.285	$131.29	$131.30	$131.30
Purchase #2	$209.75	10.478%	$231.7276	$231.73	$231.75	$231.70
Purchase #3	$31.49	7.615%	$33.888	$33.89	$33.90	$33.90
Purchase #4	$78.44	13.590%	$89.1	$89.10	$89.10	$89.10
Purchase #5	$127.80	10.486%	$141.2011	$141.20	$141.20	$141.20
Purchase #6	$155.93	4.408%	$162.8034	$162.80	$162.80	$162.80
Purchase #7	$170.37	4.602%	$178.2104	$178.21	$178.20	$178.20
7 purchase totals =	$890.67		$968.2155	$968.22	$968.25	$968.20