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	$14.46	7.423%	$15.5334	$15.53	$15.55	$15.50
Purchase #2	$47.84	4.758%	$50.1162	$50.12	$50.10	$50.10
Purchase #3	$146.89	10.381%	$162.1387	$162.14	$162.15	$162.10
Purchase #4	$59.61	10.443%	$65.8351	$65.84	$65.85	$65.80
Purchase #5	$206.41	3.617%	$213.8758	$213.88	$213.90	$213.90
Purchase #6	$171.97	7.714%	$185.2358	$185.24	$185.25	$185.20
Purchase #7	$221.29	4.190%	$230.5621	$230.56	$230.55	$230.60
7 purchase totals =	$868.47		$923.2971	$923.31	$923.35	$923.20