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	$18.31	12.599%	$20.6169	$20.62	$20.60	$20.60
Purchase #2	$218.40	4.126%	$227.4112	$227.41	$227.40	$227.40
Purchase #3	$246.70	10.171%	$271.7919	$271.79	$271.80	$271.80
Purchase #4	$49.65	11.514%	$55.3667	$55.37	$55.35	$55.40
Purchase #5	$91.29	8.702%	$99.2341	$99.23	$99.25	$99.20
Purchase #6	$188.84	9.207%	$206.2265	$206.23	$206.25	$206.20
Purchase #7	$31.57	3.234%	$32.591	$32.59	$32.60	$32.60
7 purchase totals =	$844.76		$913.2383	$913.24	$913.25	$913.20