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	$144.53	12.300%	$162.3072	$162.31	$162.30	$162.30
Purchase #2	$73.75	6.807%	$78.7702	$78.77	$78.75	$78.80
Purchase #3	$218.74	7.683%	$235.5458	$235.55	$235.55	$235.50
Purchase #4	$28.82	9.537%	$31.5686	$31.57	$31.55	$31.60
Purchase #5	$145.27	6.398%	$154.5644	$154.56	$154.55	$154.60
Purchase #6	$137.97	9.844%	$151.5518	$151.55	$151.55	$151.60
Purchase #7	$112.75	10.754%	$124.8751	$124.88	$124.90	$124.90
7 purchase totals =	$861.83		$939.1831	$939.19	$939.15	$939.30