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	$223.76	11.804%	$250.1726	$250.17	$250.15	$250.20
Purchase #2	$126.51	7.558%	$136.0716	$136.07	$136.05	$136.10
Purchase #3	$141.41	6.494%	$150.5932	$150.59	$150.60	$150.60
Purchase #4	$154.88	10.761%	$171.5466	$171.55	$171.55	$171.50
Purchase #5	$70.68	9.447%	$77.3571	$77.36	$77.35	$77.40
Purchase #6	$13.51	10.133%	$14.879	$14.88	$14.90	$14.90
Purchase #7	$199.30	11.803%	$222.8234	$222.82	$222.80	$222.80
7 purchase totals =	$930.05		$1,023.4435	$1,023.44	$1,023.40	$1,023.50