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	$75.94	3.790%	$78.8181	$78.82	$78.80	$78.80
Purchase #2	$98.64	7.593%	$106.1297	$106.13	$106.15	$106.10
Purchase #3	$109.28	11.604%	$121.9609	$121.96	$121.95	$122.00
Purchase #4	$235.43	4.251%	$245.4381	$245.44	$245.45	$245.40
Purchase #5	$33.86	13.187%	$38.3251	$38.33	$38.35	$38.30
Purchase #6	$38.79	9.498%	$42.4743	$42.47	$42.45	$42.50
Purchase #7	$194.40	11.440%	$216.6394	$216.64	$216.65	$216.60
7 purchase totals =	$786.34		$849.7856	$849.79	$849.80	$849.70