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	$15.88	12.290%	$17.8317	$17.83	$17.85	$17.80
Purchase #2	$85.38	6.120%	$90.6053	$90.61	$90.60	$90.60
Purchase #3	$209.30	3.615%	$216.8662	$216.87	$216.85	$216.90
Purchase #4	$76.58	9.381%	$83.764	$83.76	$83.75	$83.80
Purchase #5	$64.88	13.839%	$73.8587	$73.86	$73.85	$73.90
Purchase #6	$181.82	9.220%	$198.5838	$198.58	$198.60	$198.60
Purchase #7	$95.49	7.400%	$102.5563	$102.56	$102.55	$102.60
7 purchase totals =	$729.33		$784.0660	$784.07	$784.05	$784.20