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	$149.36	12.491%	$168.0166	$168.02	$168.00	$168.00
Purchase #2	$27.93	13.577%	$31.7221	$31.72	$31.70	$31.70
Purchase #3	$76.56	12.243%	$85.9332	$85.93	$85.95	$85.90
Purchase #4	$201.47	11.126%	$223.8856	$223.89	$223.90	$223.90
Purchase #5	$45.61	7.786%	$49.1612	$49.16	$49.15	$49.20
Purchase #6	$131.68	3.588%	$136.4047	$136.40	$136.40	$136.40
Purchase #7	$166.40	5.364%	$175.3257	$175.33	$175.35	$175.30
7 purchase totals =	$799.01		$870.4491	$870.45	$870.45	$870.40