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	$153.38	4.688%	$160.5705	$160.57	$160.55	$160.60
Purchase #2	$30.67	9.735%	$33.6557	$33.66	$33.65	$33.70
Purchase #3	$105.79	4.827%	$110.8965	$110.90	$110.90	$110.90
Purchase #4	$142.71	6.557%	$152.0675	$152.07	$152.05	$152.10
Purchase #5	$6.92	6.838%	$7.3932	$7.39	$7.40	$7.40
Purchase #6	$240.35	6.265%	$255.4079	$255.41	$255.40	$255.40
Purchase #7	$109.65	8.619%	$119.1007	$119.10	$119.10	$119.10
7 purchase totals =	$789.47		$839.0920	$839.10	$839.05	$839.20