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	$124.91	6.402%	$132.9067	$132.91	$132.90	$132.90
Purchase #2	$178.92	3.297%	$184.819	$184.82	$184.80	$184.80
Purchase #3	$103.45	6.803%	$110.4877	$110.49	$110.50	$110.50
Purchase #4	$168.65	8.693%	$183.3107	$183.31	$183.30	$183.30
Purchase #5	$28.38	9.577%	$31.098	$31.10	$31.10	$31.10
Purchase #6	$72.74	13.197%	$82.3395	$82.34	$82.35	$82.30
Purchase #7	$142.59	9.641%	$156.3371	$156.34	$156.35	$156.30
7 purchase totals =	$819.64		$881.2987	$881.31	$881.30	$881.20