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	$139.73	9.120%	$152.4734	$152.47	$152.45	$152.50
Purchase #2	$63.84	11.848%	$71.4038	$71.40	$71.40	$71.40
Purchase #3	$14.41	5.739%	$15.237	$15.24	$15.25	$15.20
Purchase #4	$186.55	4.572%	$195.0791	$195.08	$195.10	$195.10
Purchase #5	$105.89	5.210%	$111.4069	$111.41	$111.40	$111.40
Purchase #6	$201.35	13.430%	$228.3913	$228.39	$228.40	$228.40
Purchase #7	$73.31	13.535%	$83.2325	$83.23	$83.25	$83.20
7 purchase totals =	$785.08		$857.2240	$857.22	$857.25	$857.20