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	$185.92	6.380%	$197.7817	$197.78	$197.80	$197.80
Purchase #2	$156.87	11.851%	$175.4607	$175.46	$175.45	$175.50
Purchase #3	$134.39	8.579%	$145.9193	$145.92	$145.90	$145.90
Purchase #4	$31.77	3.341%	$32.8314	$32.83	$32.85	$32.80
Purchase #5	$227.69	13.767%	$259.0361	$259.04	$259.05	$259.00
Purchase #6	$80.64	7.774%	$86.909	$86.91	$86.90	$86.90
Purchase #7	$132.27	7.550%	$142.2564	$142.26	$142.25	$142.30
7 purchase totals =	$949.55		$1,040.1946	$1,040.20	$1,040.20	$1,040.20