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	$79.90	11.740%	$89.2803	$89.28	$89.30	$89.30
Purchase #2	$126.73	10.665%	$140.2458	$140.25	$140.25	$140.20
Purchase #3	$47.90	11.298%	$53.3117	$53.31	$53.30	$53.30
Purchase #4	$213.42	3.663%	$221.2376	$221.24	$221.25	$221.20
Purchase #5	$160.76	9.196%	$175.5435	$175.54	$175.55	$175.50
Purchase #6	$188.50	6.872%	$201.4537	$201.45	$201.45	$201.50
Purchase #7	$240.60	11.181%	$267.5015	$267.50	$267.50	$267.50
7 purchase totals =	$1,057.81		$1,148.5741	$1,148.57	$1,148.60	$1,148.50