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	$42.90	11.630%	$47.8893	$47.89	$47.90	$47.90
Purchase #2	$71.57	6.712%	$76.3738	$76.37	$76.35	$76.40
Purchase #3	$188.51	5.359%	$198.6123	$198.61	$198.60	$198.60
Purchase #4	$49.58	7.740%	$53.4175	$53.42	$53.40	$53.40
Purchase #5	$200.41	7.839%	$216.1201	$216.12	$216.10	$216.10
Purchase #6	$227.39	4.712%	$238.1046	$238.10	$238.10	$238.10
Purchase #7	$65.86	6.618%	$70.2186	$70.22	$70.20	$70.20
7 purchase totals =	$846.22		$900.7362	$900.73	$900.65	$900.70