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	$97.58	5.814%	$103.2533	$103.25	$103.25	$103.30
Purchase #2	$108.86	9.723%	$119.4445	$119.44	$119.45	$119.40
Purchase #3	$186.57	7.344%	$200.2717	$200.27	$200.25	$200.30
Purchase #4	$161.58	5.614%	$170.6511	$170.65	$170.65	$170.70
Purchase #5	$100.46	13.737%	$114.2602	$114.26	$114.25	$114.30
Purchase #6	$174.82	3.368%	$180.7079	$180.71	$180.70	$180.70
Purchase #7	$153.78	9.560%	$168.4814	$168.48	$168.50	$168.50
7 purchase totals =	$983.65		$1,057.0701	$1,057.06	$1,057.05	$1,057.20