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	$46.63	7.380%	$50.0713	$50.07	$50.05	$50.10
Purchase #2	$228.37	11.833%	$255.393	$255.39	$255.40	$255.40
Purchase #3	$82.74	7.380%	$88.8462	$88.85	$88.85	$88.80
Purchase #4	$141.78	10.334%	$156.4315	$156.43	$156.45	$156.40
Purchase #5	$158.95	3.474%	$164.4719	$164.47	$164.45	$164.50
Purchase #6	$113.97	5.215%	$119.9135	$119.91	$119.90	$119.90
Purchase #7	$81.64	7.794%	$88.003	$88.00	$88.00	$88.00
7 purchase totals =	$854.08		$923.1304	$923.12	$923.10	$923.10