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	$73.78	13.328%	$83.6134	$83.61	$83.60	$83.60
Purchase #2	$245.80	4.733%	$257.4337	$257.43	$257.45	$257.40
Purchase #3	$175.55	3.865%	$182.335	$182.34	$182.35	$182.30
Purchase #4	$152.69	6.308%	$162.3217	$162.32	$162.30	$162.30
Purchase #5	$124.97	12.498%	$140.5888	$140.59	$140.60	$140.60
Purchase #6	$208.47	7.348%	$223.7884	$223.79	$223.80	$223.80
Purchase #7	$95.92	13.793%	$109.1502	$109.15	$109.15	$109.20
7 purchase totals =	$1,077.18		$1,159.2312	$1,159.23	$1,159.25	$1,159.20