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	$171.51	11.495%	$191.2251	$191.23	$191.25	$191.20
Purchase #2	$186.61	12.495%	$209.9269	$209.93	$209.95	$209.90
Purchase #3	$203.57	8.668%	$221.2154	$221.22	$221.20	$221.20
Purchase #4	$228.84	4.192%	$238.433	$238.43	$238.45	$238.40
Purchase #5	$28.50	8.783%	$31.0032	$31.00	$31.00	$31.00
Purchase #6	$49.79	6.663%	$53.1075	$53.11	$53.10	$53.10
Purchase #7	$33.28	12.453%	$37.4244	$37.42	$37.40	$37.40
7 purchase totals =	$902.10		$982.3355	$982.34	$982.35	$982.20