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	$174.98	7.671%	$188.4027	$188.40	$188.40	$188.40
Purchase #2	$50.88	4.781%	$53.3126	$53.31	$53.30	$53.30
Purchase #3	$201.48	6.757%	$215.094	$215.09	$215.10	$215.10
Purchase #4	$52.83	12.167%	$59.2578	$59.26	$59.25	$59.30
Purchase #5	$19.43	12.194%	$21.7993	$21.80	$21.80	$21.80
Purchase #6	$185.48	5.715%	$196.0802	$196.08	$196.10	$196.10
Purchase #7	$48.90	12.534%	$55.0291	$55.03	$55.05	$55.00
7 purchase totals =	$733.98		$788.9757	$788.97	$789.00	$789.00