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	$71.79	8.508%	$77.8979	$77.90	$77.90	$77.90
Purchase #2	$78.52	13.105%	$88.81	$88.81	$88.80	$88.80
Purchase #3	$224.57	9.430%	$245.747	$245.75	$245.75	$245.70
Purchase #4	$190.50	10.522%	$210.5444	$210.54	$210.55	$210.50
Purchase #5	$239.48	7.119%	$256.5286	$256.53	$256.55	$256.50
Purchase #6	$164.59	6.496%	$175.2818	$175.28	$175.30	$175.30
Purchase #7	$115.71	13.524%	$131.3586	$131.36	$131.35	$131.40
7 purchase totals =	$1,085.16		$1,186.1683	$1,186.17	$1,186.20	$1,186.10