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	$64.32	13.152%	$72.7794	$72.78	$72.80	$72.80
Purchase #2	$216.36	11.304%	$240.8173	$240.82	$240.80	$240.80
Purchase #3	$148.60	10.782%	$164.6221	$164.62	$164.60	$164.60
Purchase #4	$98.66	13.810%	$112.2849	$112.28	$112.30	$112.30
Purchase #5	$183.47	11.376%	$204.3415	$204.34	$204.35	$204.30
Purchase #6	$64.98	13.362%	$73.6626	$73.66	$73.65	$73.70
Purchase #7	$41.96	4.207%	$43.7253	$43.73	$43.75	$43.70
7 purchase totals =	$818.35		$912.2331	$912.23	$912.25	$912.20