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	$210.55	5.858%	$222.884	$222.88	$222.90	$222.90
Purchase #2	$104.84	12.229%	$117.6609	$117.66	$117.65	$117.70
Purchase #3	$184.57	3.768%	$191.5246	$191.52	$191.50	$191.50
Purchase #4	$165.34	8.187%	$178.8764	$178.88	$178.90	$178.90
Purchase #5	$218.43	7.822%	$235.5156	$235.52	$235.50	$235.50
Purchase #6	$175.32	12.812%	$197.782	$197.78	$197.80	$197.80
Purchase #7	$115.97	13.464%	$131.5842	$131.58	$131.60	$131.60
7 purchase totals =	$1,175.02		$1,275.8277	$1,275.82	$1,275.85	$1,275.90