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	$90.37	8.782%	$98.3063	$98.31	$98.30	$98.30
Purchase #2	$10.57	10.549%	$11.685	$11.69	$11.70	$11.70
Purchase #3	$216.37	3.144%	$223.1727	$223.17	$223.15	$223.20
Purchase #4	$123.96	12.642%	$139.631	$139.63	$139.65	$139.60
Purchase #5	$7.60	11.737%	$8.492	$8.49	$8.50	$8.50
Purchase #6	$237.81	11.111%	$264.2331	$264.23	$264.25	$264.20
Purchase #7	$6.85	8.265%	$7.4162	$7.42	$7.40	$7.40
7 purchase totals =	$693.53		$752.9363	$752.94	$752.95	$752.90