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	$46.75	7.767%	$50.3811	$50.38	$50.40	$50.40
Purchase #2	$156.99	11.666%	$175.3045	$175.30	$175.30	$175.30
Purchase #3	$218.25	13.754%	$248.2681	$248.27	$248.25	$248.30
Purchase #4	$34.32	8.272%	$37.159	$37.16	$37.15	$37.20
Purchase #5	$43.61	5.380%	$45.9562	$45.96	$45.95	$46.00
Purchase #6	$52.93	9.355%	$57.8816	$57.88	$57.90	$57.90
Purchase #7	$80.61	6.140%	$85.5595	$85.56	$85.55	$85.60
7 purchase totals =	$633.46		$700.5100	$700.51	$700.50	$700.70