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	$249.82	11.459%	$278.4469	$278.45	$278.45	$278.40
Purchase #2	$62.95	12.662%	$70.9207	$70.92	$70.90	$70.90
Purchase #3	$186.57	5.180%	$196.2343	$196.23	$196.25	$196.20
Purchase #4	$245.85	11.586%	$274.3342	$274.33	$274.35	$274.30
Purchase #5	$128.77	8.364%	$139.5403	$139.54	$139.55	$139.50
Purchase #6	$100.32	11.496%	$111.8528	$111.85	$111.85	$111.90
Purchase #7	$93.81	5.220%	$98.7069	$98.71	$98.70	$98.70
7 purchase totals =	$1,068.09		$1,170.0361	$1,170.03	$1,170.05	$1,169.90