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	$99.76	3.177%	$102.9294	$102.93	$102.95	$102.90
Purchase #2	$41.32	12.193%	$46.3581	$46.36	$46.35	$46.40
Purchase #3	$146.28	13.689%	$166.3043	$166.30	$166.30	$166.30
Purchase #4	$162.90	11.476%	$181.5944	$181.59	$181.60	$181.60
Purchase #5	$39.81	7.394%	$42.7536	$42.75	$42.75	$42.80
Purchase #6	$57.43	4.214%	$59.8501	$59.85	$59.85	$59.90
Purchase #7	$146.46	9.650%	$160.5934	$160.59	$160.60	$160.60
7 purchase totals =	$693.96		$760.3833	$760.37	$760.40	$760.50