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	$131.79	3.767%	$136.7545	$136.75	$136.75	$136.80
Purchase #2	$52.58	3.289%	$54.3094	$54.31	$54.30	$54.30
Purchase #3	$57.59	5.240%	$60.6077	$60.61	$60.60	$60.60
Purchase #4	$140.74	13.147%	$159.2431	$159.24	$159.25	$159.20
Purchase #5	$215.96	11.281%	$240.3224	$240.32	$240.30	$240.30
Purchase #6	$181.37	5.616%	$191.5557	$191.56	$191.55	$191.60
Purchase #7	$24.45	13.109%	$27.6552	$27.66	$27.65	$27.70
7 purchase totals =	$804.48		$870.4480	$870.45	$870.40	$870.50