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	$123.84	11.165%	$137.6667	$137.67	$137.65	$137.70
Purchase #2	$60.30	7.589%	$64.8762	$64.88	$64.90	$64.90
Purchase #3	$159.86	11.355%	$178.0121	$178.01	$178.00	$178.00
Purchase #4	$176.92	4.478%	$184.8425	$184.84	$184.85	$184.80
Purchase #5	$29.45	10.155%	$32.4406	$32.44	$32.45	$32.40
Purchase #6	$62.74	7.143%	$67.2215	$67.22	$67.20	$67.20
Purchase #7	$28.40	10.745%	$31.4516	$31.45	$31.45	$31.50
7 purchase totals =	$641.51		$696.5112	$696.51	$696.50	$696.50