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	$127.97	6.226%	$135.9374	$135.94	$135.95	$135.90
Purchase #2	$180.41	13.808%	$205.321	$205.32	$205.30	$205.30
Purchase #3	$236.78	13.865%	$269.6095	$269.61	$269.60	$269.60
Purchase #4	$53.69	10.643%	$59.4042	$59.40	$59.40	$59.40
Purchase #5	$29.40	12.825%	$33.1706	$33.17	$33.15	$33.20
Purchase #6	$194.33	7.854%	$209.5927	$209.59	$209.60	$209.60
Purchase #7	$82.48	4.402%	$86.1108	$86.11	$86.10	$86.10
7 purchase totals =	$905.06		$999.1462	$999.14	$999.10	$999.10