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	$30.72	12.506%	$34.5618	$34.56	$34.55	$34.60
Purchase #2	$105.29	7.264%	$112.9383	$112.94	$112.95	$112.90
Purchase #3	$246.55	11.670%	$275.3224	$275.32	$275.30	$275.30
Purchase #4	$129.59	11.212%	$144.1196	$144.12	$144.10	$144.10
Purchase #5	$39.32	5.649%	$41.5412	$41.54	$41.55	$41.50
Purchase #6	$129.36	13.727%	$147.1172	$147.12	$147.10	$147.10
Purchase #7	$137.96	12.353%	$155.0022	$155.00	$155.00	$155.00
7 purchase totals =	$818.79		$910.6027	$910.60	$910.55	$910.50