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	$106.50	6.540%	$113.4651	$113.47	$113.45	$113.50
Purchase #2	$86.63	4.501%	$90.5292	$90.53	$90.55	$90.50
Purchase #3	$140.84	9.247%	$153.8635	$153.86	$153.85	$153.90
Purchase #4	$39.64	6.700%	$42.2959	$42.30	$42.30	$42.30
Purchase #5	$189.92	13.442%	$215.449	$215.45	$215.45	$215.40
Purchase #6	$133.29	11.600%	$148.7516	$148.75	$148.75	$148.80
Purchase #7	$23.61	7.518%	$25.385	$25.39	$25.40	$25.40
7 purchase totals =	$720.43		$789.7393	$789.75	$789.75	$789.80