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	$143.39	10.499%	$158.4445	$158.44	$158.45	$158.40
Purchase #2	$126.68	8.496%	$137.4427	$137.44	$137.45	$137.40
Purchase #3	$106.28	6.601%	$113.2955	$113.30	$113.30	$113.30
Purchase #4	$100.83	9.532%	$110.4411	$110.44	$110.45	$110.40
Purchase #5	$39.91	5.654%	$42.1665	$42.17	$42.15	$42.20
Purchase #6	$72.67	11.338%	$80.9093	$80.91	$80.90	$80.90
Purchase #7	$202.41	3.411%	$209.3142	$209.31	$209.30	$209.30
7 purchase totals =	$792.17		$852.0138	$852.01	$852.00	$851.90