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	$51.44	7.345%	$55.2183	$55.22	$55.20	$55.20
Purchase #2	$169.42	9.342%	$185.2472	$185.25	$185.25	$185.20
Purchase #3	$165.90	13.810%	$188.8108	$188.81	$188.80	$188.80
Purchase #4	$58.30	7.307%	$62.56	$62.56	$62.55	$62.60
Purchase #5	$54.72	13.758%	$62.2484	$62.25	$62.25	$62.20
Purchase #6	$81.33	7.717%	$87.6062	$87.61	$87.60	$87.60
Purchase #7	$23.63	7.582%	$25.4216	$25.42	$25.40	$25.40
7 purchase totals =	$604.74		$667.1125	$667.12	$667.05	$667.00