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	$77.58	3.502%	$80.2969	$80.30	$80.30	$80.30
Purchase #2	$78.47	4.730%	$82.1816	$82.18	$82.20	$82.20
Purchase #3	$56.64	9.558%	$62.0537	$62.05	$62.05	$62.10
Purchase #4	$127.44	12.529%	$143.407	$143.41	$143.40	$143.40
Purchase #5	$247.46	13.690%	$281.3373	$281.34	$281.35	$281.30
Purchase #6	$234.38	9.488%	$256.618	$256.62	$256.60	$256.60
Purchase #7	$227.85	12.365%	$256.0237	$256.02	$256.00	$256.00
7 purchase totals =	$1,049.82		$1,161.9182	$1,161.92	$1,161.90	$1,161.90