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	$26.61	6.426%	$28.32	$28.32	$28.30	$28.30
Purchase #2	$127.42	11.165%	$141.6464	$141.65	$141.65	$141.60
Purchase #3	$135.95	3.381%	$140.5465	$140.55	$140.55	$140.50
Purchase #4	$134.56	9.348%	$147.1387	$147.14	$147.15	$147.10
Purchase #5	$7.51	4.820%	$7.872	$7.87	$7.85	$7.90
Purchase #6	$118.37	4.651%	$123.8754	$123.88	$123.90	$123.90
Purchase #7	$71.48	6.608%	$76.2034	$76.20	$76.20	$76.20
7 purchase totals =	$621.90		$665.6024	$665.61	$665.60	$665.50