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	$171.80	8.568%	$186.5198	$186.52	$186.50	$186.50
Purchase #2	$166.46	5.419%	$175.4805	$175.48	$175.50	$175.50
Purchase #3	$149.97	8.359%	$162.506	$162.51	$162.50	$162.50
Purchase #4	$47.58	5.456%	$50.176	$50.18	$50.20	$50.20
Purchase #5	$115.36	6.715%	$123.1064	$123.11	$123.10	$123.10
Purchase #6	$109.99	12.112%	$123.312	$123.31	$123.30	$123.30
Purchase #7	$245.67	13.736%	$279.4152	$279.42	$279.40	$279.40
7 purchase totals =	$1,006.83		$1,100.5159	$1,100.53	$1,100.50	$1,100.50