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	$138.49	6.360%	$147.298	$147.30	$147.30	$147.30
Purchase #2	$78.67	10.486%	$86.9193	$86.92	$86.90	$86.90
Purchase #3	$102.48	13.591%	$116.4081	$116.41	$116.40	$116.40
Purchase #4	$214.42	12.297%	$240.7872	$240.79	$240.80	$240.80
Purchase #5	$52.91	7.666%	$56.9661	$56.97	$56.95	$57.00
Purchase #6	$122.72	13.525%	$139.3179	$139.32	$139.30	$139.30
Purchase #7	$74.76	10.550%	$82.6472	$82.65	$82.65	$82.60
7 purchase totals =	$784.45		$870.3438	$870.36	$870.30	$870.30