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	$28.36	12.483%	$31.9002	$31.90	$31.90	$31.90
Purchase #2	$14.83	5.456%	$15.6391	$15.64	$15.65	$15.60
Purchase #3	$232.86	5.649%	$246.0143	$246.01	$246.00	$246.00
Purchase #4	$179.82	9.450%	$196.813	$196.81	$196.80	$196.80
Purchase #5	$51.49	11.719%	$57.5241	$57.52	$57.50	$57.50
Purchase #6	$108.69	13.677%	$123.5555	$123.56	$123.55	$123.60
Purchase #7	$165.89	12.276%	$186.2547	$186.25	$186.25	$186.30
7 purchase totals =	$781.94		$857.7009	$857.69	$857.65	$857.70