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	$204.90	12.219%	$229.9367	$229.94	$229.95	$229.90
Purchase #2	$164.34	13.627%	$186.7346	$186.73	$186.75	$186.70
Purchase #3	$50.95	13.516%	$57.8364	$57.84	$57.85	$57.80
Purchase #4	$218.73	10.655%	$242.0357	$242.04	$242.05	$242.00
Purchase #5	$250.92	11.799%	$280.5261	$280.53	$280.55	$280.50
Purchase #6	$223.32	7.733%	$240.5893	$240.59	$240.60	$240.60
Purchase #7	$152.57	6.380%	$162.304	$162.30	$162.30	$162.30
7 purchase totals =	$1,265.73		$1,399.9628	$1,399.97	$1,400.05	$1,399.80