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	$48.38	12.611%	$54.4812	$54.48	$54.50	$54.50
Purchase #2	$155.39	10.457%	$171.6391	$171.64	$171.65	$171.60
Purchase #3	$139.28	12.470%	$156.6482	$156.65	$156.65	$156.60
Purchase #4	$187.31	3.129%	$193.1709	$193.17	$193.15	$193.20
Purchase #5	$174.28	6.301%	$185.2614	$185.26	$185.25	$185.30
Purchase #6	$72.43	9.224%	$79.1109	$79.11	$79.10	$79.10
Purchase #7	$250.82	7.800%	$270.384	$270.38	$270.40	$270.40
7 purchase totals =	$1,027.89		$1,110.6957	$1,110.69	$1,110.70	$1,110.70